Taq Kasra

Taq Kasra, the surviving great hall of the Sasanian palace at Ctesiphon south of Baghdad, is one of the largest brick vaults ever built. Its barrel vault forms the roof of an open-fronted hall (iwan) and is a landmark in the history of masonry roofing.

Date

The construction date is uncertain, somewhere between the 3rd and 6th centuries AD, with sources crediting Shapur I, Shapur II, Khosrow I or Khosrow II.

Dimensions

• Height: about 37 m (121 ft)
• Span: about 26 m (85 ft)
• Length: about 50 m (160 ft)
• Thickness: about 1 m (3 ft) at the crown, with supporting walls up to 7 m (23 ft) thick at the base

Building a vault without centring

Large Roman vaults were usually built over temporary timber formwork (centring). Timber was scarce in Mesopotamia, and the Taq Kasra was instead built without it. Bricks were laid leaning at roughly 18 degrees from vertical, so that the rear wall partly supported them during building, and a quick-setting mortar let each new brick be held by those already laid. The method allowed builders to roof a wide space in brick alone.

Damage and restoration

A serious flood in 1888 demolished the greater part of the building. The fallen northern wing was partly rebuilt in the 1980s, but work stopped after the 1991 Gulf War. Restoration with the University of Chicago's Diyala Project took place in 2004-2008, and a Czech firm completed further work in 2017. On 7 March 2019 part of the structure collapsed.

Significance for roofing

The Taq Kasra shows how far masonry vaulting could go in a region without long timbers. Vaulted iwans and domes remained central to roofing large spaces in later Persian architecture (see roofing-in-iran and middle-eastern-domes).