Taq Kasra: The Arch of Ctesiphon

Taq Kasra, “the Arch of Khosrow”, is the ruined throne hall of the Sasanian kings at Ctesiphon, on the Tigris south of modern Baghdad. Its great brick vault, about 25 metres wide and some 35 metres high, is the largest surviving vault of its kind from the ancient world. It is usually dated to the reign of Khosrow I in the 6th century CE, although the date is still debated, and it became the most famous symbol of fallen Persian power in Arabic and Persian poetry.

The capital on the Tigris

Ctesiphon was the winter capital of the Parthian kings and became the main seat of the Sasanians. By late Sasanian times it was a cluster of towns on both banks of the Tigris, which the Arabs later called al-Mada’in, “the cities”. Here stood the royal palaces, the treasury, and the hall in which the king of kings received ambassadors, nobles and subjects. The great iwan, a vaulted hall closed on three sides and open at the front, faced east across a courtyard. Behind it lay further halls and rooms, now mostly reduced to mounds.

Who built it, and when

The building carries no inscription, and the written sources disagree. The 10th-century historian Hamza al-Isfahani reported that it was built by Shapur I, a view the archaeologist Ernst Herzfeld favoured, but himself preferred Khosrow II. Other sources name Khosrow I, and the Arabic name, the Arch of Kisra, links it to a Khosrow without saying which. Most recent scholars, including the excavators Oscar Reuther and Giorgio Gullini, have argued for the 6th century on the style of the façade. Edward Keall, in the Encyclopaedia Iranica, concludes that the evidence is largely circumstantial and that the date remains uncertain.

A popular story says the hall was built with the labour or the booty from Khosrow I’s sack of Antioch in 540. It fits the attribution to Khosrow I but rests on no direct evidence.

How the vault was built

The hall is roofed by a single parabolic vault of fired brick. Its side walls are about 7 metres thick at the base and narrow as they rise. The Sasanian builders reduced the span a little by stepping the brick courses inward below the springing of the vault. In the upper part they laid the bricks on edge and leaning slightly backwards against the courses already set, so that each ring of brick held itself up while the mortar dried. This technique, long known in Mesopotamia and Iran, meant that the vault could be built without wooden centring, a great advantage in a country with little timber. The arch itself is about 1.8 metres thick at the base and 1.3 metres at the crown.

The façade, which once stretched for some 46 metres on either side of the arch, was covered with six tiers of blind arcades, engaged columns and niches. It may have been plastered and painted. The design has roots in earlier Parthian architecture, for example at Ashur on the Tigris.

The hall in its glory

Arabic and Persian writers describe the hall as it was in the 7th century: a throne beneath a crown so heavy that it hung from the vault on a chain, curtains closing off the king from his audience, and a great garden carpet woven with gold, silver and jewels that showed the spring in flower even in winter. After the Arab armies took Ctesiphon in 637, the carpet was cut up and divided among the victors (see The Fall of Ctesiphon). Al-Tabari says that the Arab commander Sa’d ibn Abi Waqqas prayed in the iwan, which served for a time as a mosque.

A ruin that would not fall

The caliphs who built Baghdad nearby looked at the ruins as a source of building material. Al-Tabari tells that the caliph al-Mansur, in the 760s, considered pulling the hall down to reuse its bricks, and that his minister Khalid ibn Barmak, of the Persian Barmakid family, advised against it. The ruins around the hall were quarried for centuries, but the arch survived.

A mirror of warning

For poets the arch became a lesson in the passing of power. The 9th-century Arab poet al-Buhturi wrote a celebrated ode on his visit to the ruins. In the 12th century the Persian poet Khaqani stood before it on his way to Mecca and wrote his qasida on the “Iwan of Mada’in”, which every educated Iranian knows. It opens:

هان ای دل عبرت‌بین از دیده عبر کن هان / ایوان مدائن را آیینه عبرت دان

“Look, O heart that learns from warnings, look with your eyes and learn: know the Iwan of Mada’in as a mirror of warning.”

Collapse and restoration

Travellers’ drawings and photographs from the 19th century show the arch with both wings of the façade standing. In 1888 a flood brought down about a third of the ruin, including the northern wing; the French archaeologist Marcel Dieulafoy’s photographs, published shortly before, record its earlier state. A German expedition excavated at Ctesiphon in 1928–1929, and an Italian mission made studies in the 1960s. Iraqi authorities restored the southern wing in the 1970s and began rebuilding the northern wing, work that stopped with the wars after 1980 and 1991.

In recent decades the arch has suffered from neglect, weather and the conflicts in Iraq. Part of the structure collapsed in 2019, prompting new conservation work. It remains one of the most visited monuments of pre-Islamic Iraq, and a place of special meaning for Iranian visitors. The nearby town takes its name from Salman Pak, the shrine of Salman the Persian.

For other Sasanian buildings, see Sasanian Cities, Palaces and Bridges and A History of Persian Architecture.