What does IP stand for in IP address?

An Internet Protocol address (IP address) is a numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication.
An IP address serves two principal functions: host or network interface identification and location addressing.

IP address

Internet Protocol version 4 (IPv4) defines an IP address as a 32-bit number. However, because of the growth of the Internet and the depletion of available IPv4 addresses, a new version of IP (IPv6), using 128 bits for the IP address, was developed in 1995, and standardized in. In, a final definition of the protocol was published. IPv6 deployment has been ongoing since the mid-2000s.

IP addresses are usually written and displayed in human-readable notations, such as in IPv4, and in IPv6. The size of the routing prefix of the address is designated in CIDR notation by suffixing the address with the number of significant bits, e.g.,, which is equivalent to the historically used subnet mask.

The IP address space is managed globally by the Internet Assigned Numbers Authority (IANA), and by five regional Internet registries (RIRs) responsible in their designated territories for assignment to end users and local Internet registries, such as Internet service providers. IPv4 addresses have been distributed by IANA to the RIRs in blocks of approximately 16.8 million addresses each. Each ISP or private network administrator assigns an IP address to each device connected to its network. Such assignments may be on a "static" (fixed or permanent) or "dynamic" basis, depending on its software and practices.

An IP address serves two principal functions. It identifies the host, or more specifically its network interface, and it provides the location of the host in the network, and thus the capability of establishing a path to that host. Its role has been characterized as follows: "A name indicates what we seek. An address indicates where it is. A route indicates how to get there."
The header of each IP packet contains the IP address of the sending host, and that of the destination host.

Two versions of the Internet Protocol are in common use in the Internet today. The original version of the Internet Protocol that was first deployed in 1983 in the ARPANET, the predecessor of the Internet, is Internet Protocol version 4 (IPv4).

The rapid exhaustion of IPv4 address space available for assignment to Internet service providers and end user organizations by the early 1990s, prompted the Internet Engineering Task Force (IETF) to explore new technologies to expand the addressing capability in the Internet. The result was a redesign of the Internet Protocol which became eventually known as Internet Protocol Version 6 (IPv6) in 1995.
IPv6 technology was in various testing stages until the mid-2000s, when commercial production deployment commenced.

Today, these two versions of the Internet Protocol are in simultaneous use. Among other technical changes, each version defines the format of addresses differently. Because of the historical prevalence of IPv4, the generic term "IP address" typically still refers to the addresses defined by IPv4. The gap in version sequence between IPv4 and IPv6 resulted from the assignment of version 5 to the experimental Internet Stream Protocol in 1979, which however was never referred to as IPv5.

IP networks may be divided into subnetworks in both IPv4 and IPv6. For this purpose, an IP address is recognized as consisting of two parts: the "network prefix" in the high-order bits and the remaining bits called the "rest field", "host identifier", or "interface identifier" (IPv6), used for host numbering within a network. The subnet mask or CIDR notation determines how the IP address is divided into network and host parts.

The term "subnet mask" is only used within IPv4. Both IP versions however use the CIDR concept and notation. In this, the IP address is followed by a slash and the number (in decimal) of bits used for the network part, also called the "routing prefix". For example, an IPv4 address and its subnet mask may be and, respectively. The CIDR notation for the same IP address and subnet is, because the first 24 bits of the IP address indicate the network and subnet.

An IPv4 address has a size of 32 bits, which limits the address space to (2) addresses. Of this number, some addresses are reserved for special purposes such as private networks (~18 million addresses) and multicast addressing (~270 million addresses).

IPv4 addresses are usually represented in dot-decimal notation, consisting of four decimal numbers, each ranging from 0 to 255, separated by dots, e.g.,. Each part represents a group of 8 bits (an octet) of the address. In some cases of technical writing, IPv4 addresses may be presented in various hexadecimal, octal, or binary representations.

In the early stages of development of the Internet Protocol, the network number was always the highest order octet (most significant eight bits). Because this method allowed for only 256 networks, it soon proved inadequate as additional networks developed that were independent of the existing networks already designated by a network number. In 1981, the addressing specification was revised with the introduction of classful network architecture.

Classful network design allowed for a larger number of individual network assignments and fine-grained subnetwork design. The first three bits of the most significant octet of an IP address were defined as the "class" of the address. Three classes ("A", "B", and "C") were defined for universal unicast addressing. Depending on the class derived, the network identification was based on octet boundary segments of the entire address. Each class used successively additional octets in the network identifier, thus reducing the possible number of hosts in the higher order classes ("B" and "C"). The following table gives an overview of this now obsolete system.

Classful network design served its purpose in the startup stage of the Internet, but it lacked scalability in the face of the rapid expansion of networking in the 1990s. The class system of the address space was replaced with Classless Inter-Domain Routing (CIDR) in 1993. CIDR is based on variable-length subnet masking (VLSM) to allow allocation and routing based on arbitrary-length prefixes. Today, remnants of classful network concepts function only in a limited scope as the default configuration parameters of some network software and hardware components (e.g. netmask), and in the technical jargon used in network administrators' discussions.

Early network design, when global end-to-end connectivity was envisioned for communications with all Internet hosts, intended that IP addresses be globally unique. However, it was found that this was not always necessary as private networks developed and public address space needed to be conserved.

Computers not connected to the Internet, such as factory machines that communicate only with each other via TCP/IP, need not have globally unique IP addresses. Today, such private networks are widely used and typically connect to the Internet with network address translation (NAT), when needed.

Three non-overlapping ranges of IPv4 addresses for private networks are reserved. These addresses are not routed on the Internet and thus their use need not be coordinated with an IP address registry. Any user may use any of the reserved blocks. Typically, a network administrator will divide a block into subnets; for example, many home routers automatically use a default address range of through ().

In IPv6, the address size was increased from 32 bits in IPv4 to 128 bits, thus providing up to 2 (approximately ) addresses. This is deemed sufficient for the foreseeable future.

The intent of the new design was not to provide just a sufficient quantity of addresses, but also redesign routing in the Internet by allowing more efficient aggregation of subnetwork routing prefixes. This resulted in slower growth of routing tables in routers. The smallest possible individual allocation is a subnet for 2 hosts, which is the square of the size of the entire IPv4 Internet. At these levels, actual address utilization ratios will be small on any IPv6 network segment. The new design also provides the opportunity to separate the addressing infrastructure of a network segment, i.e. the local administration of the segment's available space, from the addressing prefix used to route traffic to and from external networks. IPv6 has facilities that automatically change the routing prefix of entire networks, should the global connectivity or the routing policy change, without requiring internal redesign or manual renumbering.

The large number of IPv6 addresses allows large blocks to be assigned for specific purposes and, where appropriate, to be aggregated for efficient routing. With a large address space, there is no need to have complex address conservation methods as used in CIDR.

All modern desktop and enterprise server operating systems include native support for the IPv6 protocol, but it is not yet widely deployed in other devices, such as residential networking routers, voice over IP (VoIP) and multimedia equipment, and some networking hardware.

Just as IPv4 reserves addresses for private networks, blocks of addresses are set aside in IPv6. In IPv6, these are referred to as unique local addresses (ULAs). The routing prefix is reserved for this block, which is divided into two blocks with different implied policies. The addresses include a 40-bit pseudorandom number that minimizes the risk of address collisions if sites merge or packets are misrouted.

Early practices used a different block for this purpose (), dubbed site-local addresses. However, the definition of what constituted a "site" remained unclear and the poorly-defined addressing policy created ambiguities for routing. This address type was abandoned and must not be used in new systems.

Addresses starting with, called Link-local addresses, are assigned to interfaces for communication on the attached link. The addresses are automatically generated by the operating system for each network interface. This provides instant and automatic communication between all IPv6 host on a link. This feature is used in the lower layers of IPv6 network administration, such as for the Neighbor Discovery Protocol.

Private and link-local address prefixes may not be routed on the public Internet.

IP addresses are assigned to a host either dynamically at the time of booting, or permanently by fixed configuration of the host hardware or software. Persistent configuration is also known as using a "static IP address". In contrast, when a computer's IP address is assigned newly each time it restarts, this is known as using a "dynamic IP address".

The configuration of a static IP address depends in detail on the software or hardware installed in the computer. Computers used for the network infrastructure, such as routers and mail servers, are typically configured with static addressing, Static addresses are also sometimes convenient for locating servers inside an enterprise.

Dynamic IP addresses are assigned using methods such as Zeroconf for self-configuration, or by the Dynamic Host Configuration Protocol (DHCP) from a network server. The address assigned with DHCP usually has an expiration period, after which the address may be assigned to another device, or to the originally associated host if it is still powered up. A network administrator may implement a DHCP method so that the same host always receives a specific address.

DHCP is the most frequently used technology for assigning addresses. It avoids the administrative burden of assigning specific static addresses to each device on a network. It also allows devices to share the limited address space on a network if only some of them are online at a particular time. Typically, dynamic IP configuration is enabled by default in modern desktop operating systems. DHCP is not the only technology used to assign IP addresses dynamically. Dialup and some broadband networks use dynamic address features of the Point-to-Point Protocol.

In the absence or failure of static or stateful (DHCP) address configurations, an operating system may assign an IP address to a network interface using stateless auto-configuration methods, such as Zeroconf.

A "sticky dynamic IP address" is an informal term used by cable and DSL Internet access subscribers to describe a dynamically assigned IP address which seldom changes. The addresses are usually assigned with DHCP. Since the modems are usually powered on for extended periods of time, the address leases are usually set to long periods and simply renewed. If a modem is turned off and powered up again before the next expiration of the address lease, it often receives the same IP address.

Address block is defined for the special use in link-local addressing for IPv4 networks.
In IPv6, every interface, whether using static or dynamic address assignments, also receives a link-local address automatically in the block.

These addresses are only valid on the link, such as a local network segment or point-to-point connection, that a host is connected to. These addresses are not routable and like private addresses cannot be the source or destination of packets traversing the Internet.

When the link-local IPv4 address block was reserved, no standards existed for mechanisms of address autoconfiguration. Filling the void, Microsoft created an implementation that is called Automatic Private IP Addressing (APIPA). APIPA has been deployed on millions of machines and has, thus, become a de facto standard in the industry.
Many years later, in May 2005, the IETF defined a formal standard for it.

An IP address conflict occurs when two devices on the same local physical or wireless network claim to have the same IP address. A second assignment of an address generally stops the IP functionality of one or both of the devices. Many modern operating systems notify the administrator of IP address conflicts. If one of the devices is the gateway, the network will be crippled. When IP addresses are assigned by multiple people and systems with differing methods, any of them may be at fault.

IP addresses are classified into several classes of operational characteristics: unicast, multicast, anycast and broadcast addressing.

The most common concept of an IP address is in unicast addressing, available in both IPv4 and IPv6. It normally refers to a single sender or a single receiver, and can be used for both sending and receiving. Usually, a unicast address is associated with a single device or host, but a device or host may have more than one unicast address. Some individual PCs have several distinct unicast addresses, each for its own distinct purpose. Sending the same data to multiple unicast addresses requires the sender to send all the data many times over, once for each recipient.

Broadcasting is an addressing technique available in IPv4 to send data to all possible destinations on a network in one transmission operation, while all receivers capture the network packet ("all-hosts broadcast"). The address is used for network broadcast. In addition, a directed (limited) broadcast uses the all-ones host address with the network prefix. For example, the destination address used for directed broadcast to devices on the network is.

IPv6 does not implement broadcast addressing, and replaces it with multicast to the specially-defined all-nodes multicast address.

A multicast address is associated with a group of interested receivers. In IPv4, addresses through (the former Class D addresses) are designated as multicast addresses. IPv6 uses the address block with the prefix for multicast applications. In either case, the sender sends a single datagram from its unicast address to the multicast group address and the intermediary routers take care of making copies and sending them to all receivers that have joined the corresponding multicast group.

Like broadcast and multicast, anycast is a one-to-many routing topology. However, the data stream is not transmitted to all receivers, just the one which the router decides is logically closest in the network. Anycast address is an inherent feature of only IPv6. In IPv4, anycast addressing implementations typically operate using the shortest-path metric of BGP routing and do not take into account congestion or other attributes of the path. Anycast methods are useful for global load balancing and are commonly used in distributed DNS systems.

A host may use geolocation software to deduce the geolocation of its communicating peer.
A public IP address, in common parlance, is a globally routable unicast IP address, meaning that the address is not an address reserved for use in private networks, such as those reserved by, or the various IPv6 address formats of local scope or site-local scope, for example for link-local addressing. Public IP addresses may be used for communication between hosts on the global Internet.

For security and privacy considerations, network administrators often desire to restrict public Internet traffic within their private networks. The source and destination IP addresses contained in the headers of each IP packet are a convenient means to discriminate traffic by IP address blocking or by selectively tailoring responses to external requests to internal servers. This is achieved with firewall software running on the networks gateway router. A database of IP addresses of permissible traffic may be maintained in blacklists or whitelists.

Multiple client devices can appear to share an IP address, either because they are part of a shared hosting web server environment or because an IPv4 network address translator (NAT) or proxy server acts as an intermediary agent on behalf of the client, in which case the real originating IP address might be masked from the server receiving a request. A common practice is to have a NAT mask a large number of devices in a private network. Only the "outside" interface(s) of the NAT needs to have an Internet-routable address.

Commonly, the NAT device maps TCP or UDP port numbers on the side of the larger, public network to individual private addresses on the masqueraded network.

In residential networks, NAT functions are usually implemented in a residential gateway. In this scenario, the computers connected to the router have private IP addresses and the router has a public address on its external interface to communicate on the Internet. The internal computers appear to share one public IP address.

Computer operating systems provide various diagnostic tools to examine their network interface and address configuration. Windows provides the command-line interface tools ipconfig and netsh and users of Unix-like systems can use ifconfig, netstat, route, lanstat, fstat, or iproute2 utilities to accomplish the task.


When was Persepolis founded?

Darius I built the greatest palace at Persepolis on the western side of platform. This palace was called the "Apadana". The King of Kings used it for official audiences. The work began in 518 BC, and his son, Xerxes I, completed it 30 years later. The palace had a grand hall in the shape of a square, each side long with seventy-two columns, thirteen of which still stand on the enormous platform. Each column is high with a square Taurus (bull) and plinth. The columns carried the weight of the vast and heavy ceiling. The tops of the columns were made from animal sculptures such as two-headed lions, eagles, human beings and cows (cows were symbols of fertility and abundance in ancient Iran). The columns were joined to each other with the help of oak and cedar beams, which were brought from Lebanon. The walls were covered with a layer of mud and stucco to a depth of 5 cm, which was used for bonding, and then covered with the greenish stucco which is found throughout the palaces.

Persepolis

Persepolis (, ) was the ceremonial capital of the Achaemenid Empire (). It is situated northeast of the city of Shiraz in Fars Province, Iran. The earliest remains of Persepolis date back to 515 BCE. It exemplifies the Achaemenid style of architecture. UNESCO declared the ruins of Persepolis a World Heritage Site in 1979.

The English word "" is derived from Greek "Persépolis" (), a compound of "Pérsēs" () and "pólis" (), meaning "the Persian city" or "the city of the Persians". To the ancient Persians, the city was known as "Pārsa" (), which is also the word for the region of Persia.

An inscription left by Sasanian prince Shapur Sakanshah, the son of Hormizd II, refers to the site as, meaning "Hundred Pillars". Because medieval Persians attributed the site to Jamshid, an Iranian mythological king, it has been referred to as "Takht-e-Jamshid" (, ; ), literally meaning "Throne of Jamshid". Another name given to the site in the medieval period was, literally meaning "Forty Minarets".

Persepolis is near the small river Pulvar, which flows into the Kur River.

The site includes a 125,000 square meter terrace, partly artificially constructed and partly cut out of a mountain, with its east side leaning on Rahmat Mountain. The other three sides are formed by retaining walls, which vary in height with the slope of the ground. Rising from on the west side was a double stair. From there, it gently slopes to the top. To create the level terrace, depressions were filled with soil and heavy rocks, which were joined together with metal clips.

Archaeological evidence shows that the earliest remains of Persepolis date back to 515 BC. André Godard, the French archaeologist who excavated Persepolis in the early 1930s, believed that it was Cyrus the Great who chose the site of Persepolis, but that it was Darius I who built the terrace and the palaces. Inscriptions on these buildings support the belief that they were constructed by Darius.

With Darius I, the scepter passed to a new branch of the royal house. Persepolis probably became the capital of Persia proper during his reign. However, the city's location in a remote and mountainous region made it an inconvenient residence for the rulers of the empire. The country's true capitals were Susa, Babylon and Ecbatana. This may be why the Greeks were not acquainted with the city until Alexander the Great took and plundered it.

Darius I's construction of Persepolis were carried out parallel to those of the Palace of Susa. According to Gene R. Garthwaite, the Susa Palace served as Darius' model for Persepolis. Darius I ordered the construction of the Apadana and the Council Hall ("Tripylon" or the "Triple Gate"), as well as the main imperial Treasury and its surroundings. These were completed during the reign of his son, Xerxes I. Further construction of the buildings on the terrace continued until the downfall of the Achaemenid Empire. According to the Encyclopædia Britannica, the Greek historian Ctesias mentioned that Darius I's grave was in a cliff face that could be reached with an apparatus of ropes.

Around 519 BC, construction of a broad stairway was begun. The stairway was initially planned to be the main entrance to the terrace above the ground. The dual stairway, known as the Persepolitan Stairway, was built symmetrically on the western side of the Great Wall. The 111 steps measured wide, with treads of and rises of. Originally, the steps were believed to have been constructed to allow for nobles and royalty to ascend by horseback. New theories, however, suggest that the shallow risers allowed visiting dignitaries to maintain a regal appearance while ascending. The top of the stairways led to a small yard in the north-eastern side of the terrace, opposite the Gate of All Nations.

Grey limestone was the main building material used at Persepolis. After natural rock had been leveled and the depressions filled in, the terrace was prepared. Major tunnels for sewage were dug underground through the rock. A large elevated water storage tank was carved at the eastern foot of the mountain. Professor Olmstead suggested the cistern was constructed at the same time that construction of the towers began.

The uneven plan of the terrace, including the foundation, acted like a castle, whose angled walls enabled its defenders to target any section of the external front. Diodorus Siculus writes that Persepolis had three walls with ramparts, which all had towers to provide a protected space for the defense personnel. The first wall was tall, the second, and the third wall, which covered all four sides, was in height, though no presence of the wall exists in modern times.

The function of Persepolis remains rather unclear. It was not one of the largest cities in Persia, let alone the rest of the empire, but appears to have been a grand ceremonial complex, that was only occupied seasonally; it is still not entirely clear where the king's private quarters actually were. Until recent challenges, most archaeologists held that it was especially used for celebrating Nowruz, the Persian New Year, held at the spring equinox, and still an important annual festivity in modern Iran. The Iranian nobility and the tributary parts of the empire came to present gifts to the king, as represented in the stairway reliefs.

After invading Achaemenid Persia in 330 BC, Alexander the Great sent the main force of his army to Persepolis by the Royal Road. He stormed the "Persian Gates", a pass through modern-day Zagros Mountains. There Ariobarzanes of Persis successfully ambushed Alexander the Great's army, inflicting heavy casualties. After being held off for 30 days, Alexander the Great outflanked and destroyed the defenders. Ariobarzanes himself was killed either during the battle or during the retreat to Persepolis. Some sources indicate that the Persians were betrayed by a captured tribal chief who showed the Macedonians an alternate path that allowed them to outflank Ariobarzanes in a reversal of Thermopylae. After several months, Alexander allowed his troops to loot Persepolis.
Around that time, a fire burned "the palaces" or "the palace". Scholars agree that this event, described in historic sources, occurred at the ruins that have been now re-identified as Persepolis. From Stolze's investigations, it appears that at least one of these, the castle built by Xerxes I, bears traces of having been destroyed by fire. The locality described by Diodorus Siculus after Cleitarchus corresponds in important particulars with the historic Persepolis, for example, in being supported by the mountain on the east.

It is believed that the fire which destroyed Persepolis started from Hadish Palace, which was the living quarters of Xerxes I, and spread to the rest of the city. It is not clear if the fire was an accident or a deliberate act of revenge for the burning of the Acropolis of Athens during the second Persian invasion of Greece. Many historians argue that, while Alexander's army celebrated with a symposium, they decided to take revenge against the Persians. If that is so, then the destruction of Persepolis could be both an accident and a case of revenge.

The "Book of Arda Wiraz", a Zoroastrian work composed in the 3rd or 4th century, describes Persepolis' archives as containing "all the Avesta and Zend, written upon prepared cow-skins, and with gold ink", which were destroyed. Indeed, in his "Chronology of the Ancient Nations", the native Iranian writer Biruni indicates unavailability of certain native Iranian historiographical sources in the post-Achaemenid era, especially during the Parthian Empire. He adds: "[Alexander] burned the whole of Persepolis as revenge to the Persians, because it seems the Persian King Xerxes had burnt the Greek City of Athens around 150 years ago. People say that, even at the present time, the traces of fire are visible in some places."

Paradoxically, the event that caused the destruction of these texts may have resulted in the preservation of the Persepolis Administrative Archives, which might otherwise have been lost over time to natural and man-made events. According to archaeological evidence, the partial burning of Persepolis did not affect what are now referred to as the "Persepolis Fortification Archive" tablets, but rather may have caused the eventual collapse of the upper part of the northern fortification wall that preserved the tablets until their recovery by the Oriental Institute's archaeologists.

In 316 BC, Persepolis was still the capital of Persia as a province of the great Macedonian Empire (see Diod. xix, 21 seq., 46; probably after Hieronymus of Cardia, who was living about 326). The city must have gradually declined in the course of time. The lower city at the foot of the imperial city might have survived for a longer time; but the ruins of the Achaemenids remained as a witness to its ancient glory. It is probable that the principal town of the country, or at least of the district, was always in this neighborhood.

About 200 BC, the city of Estakhr, five kilometers north of Persepolis, was the seat of the local governors. From there, the foundations of the second great Persian Empire were laid, and there Estakhr acquired special importance as the center of priestly wisdom and orthodoxy. The Sasanian kings have covered the face of the rocks in this neighborhood, and in part even the Achaemenid ruins, with their sculptures and inscriptions. They must themselves have been built largely there, although never on the same scale of magnificence as their ancient predecessors. The Romans knew as little about Estakhr as the Greeks had known about Persepolis, despite the fact that the Sasanians maintained relations for four hundred years, friendly or hostile, with the empire.

At the time of the Muslim invasion of Persia, Estakhr offered a desperate resistance. It was still a place of considerable importance in the first century of Islam, although its greatness was speedily eclipsed by the new metropolis of Shiraz. In the 10th century, Estakhr dwindled to insignificance, as seen from the descriptions of Estakhri, a native (c. 950), and of Al-Muqaddasi (c. 985). During the following centuries, Estakhr gradually declined, until it ceased to exist as a city.

Odoric of Pordenone passed through Persepolis on his way to China in 1320. In 1474, Giosafat Barbaro visited the ruins of Persepolis, which he incorrectly thought were of Jewish origin. António de Gouveia from Portugal wrote about cuneiform inscriptions following his visit in 1602. His first written report on Persia, the "Jornada", was published in 1606.

In 1618, García de Silva Figueroa, King Philip III of Spain's ambassador to the court of Abbas I, the Safavid monarch, was the first Western traveler to correctly identify the ruins of Persepolis as the location of Persepolis.

Pietro Della Valle visited Persepolis in 1621, and noticed that only 25 of the 72 original columns were still standing, due to either vandalism or natural processes. The Dutch traveler Cornelis de Bruijn visited Persepolis in 1704.

The fruitful region was covered with villages until its frightful devastation in the 18th century; and even now it is, comparatively speaking, well cultivated. The Castle of Estakhr played a conspicuous part as a strong fortress, several times, during the Muslim period. It was the middlemost and the highest of the three steep crags which rise from the valley of the Kur, at some distance to the west or northwest of the necropolis of Naqsh-e Rustam.

French voyagers Eugène Flandin and Pascal Coste are among the first to provide not only a literary review of the structure of Persepolis, but also to create some of the best and earliest visual depictions of its structure. In their publications in Paris, in 1881 and 1882, titled "Voyages en Perse de MM. Eugene Flanin peintre et Pascal Coste architecte", the authors provided some 350 ground breaking illustrations of Persepolis. French influence and interest in Persia's archaeological findings would not end until the time of Reza Shah, when such distinguished figures as André Godard helped create Iran's first heritage museum.

Throughout the 1800s and early 1900s, a variety of amateur digging occurred at the site, in some cases on a large scale.

The first scientific excavations at Persepolis were carried out by Ernst Herzfeld and Erich Schmidt representing the Oriental Institute of the University of Chicago. They conducted excavations for eight seasons, beginning in 1930, and included other nearby sites.
Herzfeld believed that the reasons behind the construction of Persepolis were the need for a majestic atmosphere, a symbol for the empire, and to celebrate special events, especially the "Nowruz". For historical reasons, Persepolis was built where the Achaemenid dynasty was founded, although it was not the center of the empire at that time.

Excavations of plaque fragments hint at a scene with a contest between Herakles and Apollo, dubbed "A Greek painting at Persepolis".

Persepolitan architecture is noted for its use of the Persian column, which was probably based on earlier wooden columns. Architects resorted to stone only when the largest cedars of Lebanon or teak trees of India did not fulfill the required sizes. Column bases and capitals were made of stone, even on wooden shafts, but the existence of wooden capitals is probable.

The buildings at Persepolis include three general groupings: military quarters, the treasury, and the reception halls and occasional houses for the King. Noted structures include the Great Stairway, the Gate of All Nations, the Apadana, the Hall of a Hundred Columns, the Tripylon Hall and the Tachara, the Hadish Palace, the Palace of Artaxerxes III, the Imperial Treasury, the Royal Stables, and the Chariot House.

Ruins of a number of colossal buildings exist on the terrace. All are constructed of dark-grey marble. Fifteen of their pillars stand intact. Three more pillars have been re-erected since 1970. Several of the buildings were never finished. F. Stolze has shown that some of the mason's rubbish remains.

Since the time of Pietro Della Valle, it has been beyond dispute that these ruins represent the Persepolis captured and partly destroyed by Alexander the Great.

Behind the compound at Persepolis, there are three sepulchers hewn out of the rock in the hillside. The facades, one of which is incomplete, are richly decorated with reliefs. About 13 km NNE, on the opposite side of the Pulvar River, rises a perpendicular wall of rock, in which four similar tombs are cut at a considerable height from the bottom of the valley. Modern-day Iranians call this place "Naqsh-e Rustam" ("Rustam Relief"), from the Sasanian reliefs beneath the opening, which they take to be a representation of the mythical hero Rostam. It may be inferred from the sculptures that the occupants of these seven tombs were kings. An inscription on one of the tombs declares it to be that of Darius I, concerning whom Ctesias relates that his grave was in the face of a rock, and could only be reached by the use of ropes. Ctesias mentions further, with regard to a number of Persian kings, either that their remains were brought "to the Persians," or that they died there.

The Gate of All Nations, referring to subjects of the empire, consisted of a grand hall that was a square of approximately in length, with four columns and its entrance on the Western Wall. There were two more doors, one to the south which opened to the Apadana yard and the other opened onto a long road to the east. Pivoting devices found on the inner corners of all the doors indicate that they were two-leafed doors, probably made of wood and covered with sheets of ornate metal.

A pair of lamassus, bulls with the heads of bearded men, stand by the western threshold. Another pair, with wings and a "Persian Head" ("Gopät-Shäh"), stands by the eastern entrance, to reflect the power of the empire.

The name of Xerxes I was written in three languages and carved on the entrances, informing everyone that he ordered it to be built.

Foundation tablets of gold and silver were found in two deposition boxes in the foundations of the Palace. They contained an inscription by Darius in Old Persian cuneiform, which describes the extent of his Empire in broad geographical terms, and is known as the DPh inscription:

At the western, northern and eastern sides of the palace, there were three rectangular porticos each of which had twelve columns in two rows of six. At the south of the grand hall, a series of rooms were built for storage. Two grand Persepolitan stairways were built, symmetrical to each other and connected to the stone foundations. To protect the roof from erosion, vertical drains were built through the brick walls. In the four corners of Apadana, facing outwards, four towers were built.

The walls were tiled and decorated with pictures of lions, bulls, and flowers. Darius ordered his name and the details of his empire to be written in gold and silver on plates, which were placed in covered stone boxes in the foundations under the Four Corners of the palace. Two Persepolitan style symmetrical stairways were built on the northern and eastern sides of Apadana to compensate for a difference in level. Two other stairways stood in the middle of the building. The external front views of the palace were embossed with carvings of the Immortals, the Kings' elite guards. The northern stairway was completed during the reign of Darius I, but the other stairway was completed much later.

The reliefs on the staircases allow one to observe the people from across the empire in their traditional dress, and even the king himself, "down to the smallest detail".

The Apadana hoard is a hoard of coins that were discovered under the stone boxes containing the foundation tablets of the Apadana Palace in Persepolis. The coins were discovered in excavations in 1933 by Erich Schmidt, in two deposits, each deposit under the two deposition boxes that were found. The deposition of this hoard is dated to circa 515 BCE. The coins consisted in eight gold lightweight Croeseids, a tetradrachm of Abdera, a stater of Aegina and three double-sigloi from Cyprus. The Croeseids were found in very fresh condition, confirming that they had been recently minted under Achaemenid rule. The deposit did not have any Darics and Sigloi, which also suggests strongly that these coins typical of Achaemenid coinage only started to be minted later, after the foundation of the Apadana Palace.

Next to the Apadana, second largest building of the Terrace and the final edifices, is the Throne Hall or the Imperial Army's "Hall of Honor" (also called the "Hundred-Columns Palace"). This 70x70 square meter hall was started by Xerxes I and completed by his son Artaxerxes I by the end of the fifth century BC. Its eight stone doorways are decorated on the south and north with reliefs of throne scenes and on the east and west with scenes depicting the king in combat with monsters. Two colossal stone bulls flank the northern portico. The head of one of the bulls now resides in the Oriental Institute in Chicago.

At the beginning of the reign of Xerxes I, the Throne Hall was used mainly for receptions for military commanders and representatives of all the subject nations of the empire. Later, the Throne Hall served as an imperial museum.

Other palaces included the Tachara, which was built under Darius I, and the Imperial treasury, which was started by Darius I in 510 BC and finished by Xerxes I in 480 BC. The Hadish Palace of Xerxes I occupies the highest level of terrace and stands on the living rock. The Council Hall, the Tryplion Hall, the Palaces of D, G, H, storerooms, stables and quarters, the unfinished gateway and a few miscellaneous structures at Persepolis are located near the south-east corner of the terrace, at the foot of the mountain.

It is commonly accepted that Cyrus the Great was buried in Pasargadae, which is mentioned by Ctesias as his own city. If it is true that the body of Cambyses II was brought home "to the Persians," his burying place must be somewhere beside that of his father. Ctesias assumes that it was the custom for a king to prepare his own tomb during his lifetime. Hence, the kings buried at Naghsh-e Rostam are probably Darius I, Xerxes I, Artaxerxes I and Darius II. Xerxes II, who reigned for a very short time, could scarcely have obtained so splendid a monument, and still less could the usurper Sogdianus. The two completed graves behind the compound at Persepolis would then belong to Artaxerxes II and Artaxerxes III. The unfinished tomb, a kilometer away from the city, is debated to who it belongs. It is perhaps that of Artaxerxes IV, who reigned at the longest two years, or, if not his, then that of Darius III (Codomannus), who is one of those whose bodies are said to have been brought "to the Persians." Since Alexander the Great is said to have buried Darius III at Persepolis, then it is likely the unfinished tomb is his.

Another small group of ruins in the same style is found at the village of Haji Abad, on the Pulvar River, a good hour's walk above Persepolis. These formed a single building, which was still intact 900 years ago, and was used as the mosque of the then-existing city of Estakhr.

The relevant passages from ancient scholars on the subject are set out below:

There is, however, one formidable difficulty. Diodorus Siculus says that the rock at the back of the palace containing the royal sepulchers is so steep that the bodies could be raised to their last resting-place only by mechanical appliances. This is not true of the graves behind the compound, to which, as F. Stolze expressly observes, one can easily ride up. On the other hand, it is strictly true of the graves at Naqsh-e Rustam. Stolze accordingly started the theory that the royal castle of Persepolis stood close by Naqsh-e Rustam, and has sunk in course of time to shapeless heaps of earth, under which the remains may be concealed.

In 1971, Persepolis was the main staging ground for the "2,500 Year Celebration of the Persian Empire" under the reign of the Pahlavi dynasty. It included delegations from foreign nations in an attempt to advance the Iranian culture and history.

Construction of the Sivand Dam, named after the nearby town of Sivand, began on 19 September 2006. Despite 10 years of planning, Iran's Cultural Heritage Organization was not aware of the broad areas of flooding during much of this time, and there is growing concern about the effects the dam will have on the surrounding areas of Persepolis.

Many archaeologists worry that the dam's placement between the ruins of Pasargadae and Persepolis will flood both. Engineers involved with the construction deny this claim, stating that it is impossible, because both sites sit well above the planned waterline. Of the two sites, Pasargadae is considered the more threatened.

Archaeologists are also concerned that an increase in humidity caused by the lake will speed Pasargadae's gradual destruction. However, experts from the Ministry of Energy believe this would be negated by controlling the water level of the dam reservoir.

A number of bas-reliefs from Persepolis are kept at the Fitzwilliam Museum in Cambridge, England. There is also a collection from Persepolis at the British Museum. The Persepolis bull at the Oriental Institute is one of the university's most prized treasures, but it is only one of several objects from Persepolis on display at the University of Chicago. New York City's Metropolitan Museum houses objects from Persepolis, as does the Museum of Archaeology and Anthropology of the University of Pennsylvania. The Museum of Fine Arts of Lyon and the Louvre of Paris hold objects from Persepolis as well.