Hauran Basalt Corbelled Roofs

In the Hauran (Hawrān), the volcanic basalt region straddling southern Syria and northern Jordan, Roman and late antique builders roofed houses, churches and baths almost entirely in stone. Basalt is strong in compression and there was little timber, so roofs were made of long, thin basalt slabs carried on projecting stone corbels or on stone arches. The town of Umm el-Jimal in Jordan, and Bosra in Syria, are key examples.

Corbel-and-slab roofs

Corbels were set into the walls so that they projected inward, often two or three rows one above another. Long basalt slabs were then laid from corbel tip to corbel tip, and thin slabs covered the remaining gap. This system roofed single- and multi-storey buildings and both rectangular and semicircular rooms. Corbels were set into pockets in the bearing walls to a depth of the full wall thickness or half of it.

Arch-and-slab roofs

For wider rooms, builders spanned the space with transverse arches of small dry-laid blocks and laid long, thin slabs between them, a method described as the "arches supporting stone slab system". Big arches were often tied to internal buttresses that carried their thrust down to the ground. Lightweight volcanic scoria was used for vaults and domes, with hydraulic lime mortar containing scoria.

Dated examples

• Bosra, South Bath (Syria): 2nd-3rd century AD, with a semidome under a flat basalt slab.
• Umm el-Jimal (Jordan): the Barracks Chapel has a corbelled flat apse roof built about a year after the Julianos Church of 345 AD. The town had about 15 churches in late antiquity.
• Lubbēn Large Church: 417 AD, with a flat-roofed apse on transverse arches.
• Bosra Cathedral: 512-513 AD.

A major earthquake in 747 AD destroyed Umm el-Jimal. Because so many basalt buildings still stand roofless or partly roofed, the Hauran is an important region for the study of ancient stone roofing.

Context

These roofs are a stone relative of the corbelled timber darbazi roofs of Georgia and the corbelled domes found elsewhere. Their tall basalt walls also allowed buildings of two or three storeys.