Umm el-Jimal

Building in Basalt

Amman: Al-Kutba. 1990. Pg. 9.

Bert de Vries

The beauty of Umm el-Jimal is in its simplicity, in the no-nonsense practicality of its buildings. The priority was affordable, durable, livable houses, not colonnaded streets and ornate monuments.

While Jerash was built almost exclusively of limestone, Umm el-Jimal was constructed entirely with black basalt. Basalt, the solidified lava of volcanic emissions, is extremely hard, has great tensile strength and is much more resistant to erosion. That it was difficult to cut and dress dictated simple building techniques and resulted in these distinctive architectural features:

Corbeling

Corbeling is the use of cantilevered ceiling and roof supports designed to carry stone or wooden beams. The community knew the barrel vault and the arch. However, corbeled ceiling supports avoided the erection of elaborate scaffolding and the cutting of finely dressed and precisely curved blocks.

Corbels could hold a considerable load without cracking and were held in place by the weight of the walls of the floors above. The length of the stone ceiling beams placed on the corbels was limited to about three meters. The result was a rather narrow room of indefinite length. To create larger halls, well-constructed arches five to ten meters in width were used. Almost every private house had one large room with an arched partition, while a number of church auditoriums used a row of these transverse partitions to create a hall-size space.

Cantilevered Stairways

Basalt also lent itself to the cantilevering of stairway treads along walls. Because of the narrowness of the rooms, the stairs usually were constructed on the outside, particularly in the courtyards of buildings. The 45-degree slope of the stairs with the horizontal stoops in front of upper story doorways produces an interesting pattern of aesthetic balance.

Building Quality

Their remarkable state of preservation indicates that, despite the rough appearance, most buildings were well built. The majority of walls are of a simple rubble-filled type. The two faces were built independently, of stones dressed only on the exterior. The interior space between the double wall was filled with small stone chips and soil as construction progressed.

The two faces of such a wall were tied together only by ceiling corbels and stairway treads, which extend all the way through both faces. The combination of building blocks and rubble formed a solid mass, which remained very strong as long as the plaster joints retained the interior rubble. With the plaster gone, however, the rubble would dribble out over time, leaving a hollow core.

In this condition, the standing wall faces become very unstable and tend to pop outward if the equilibrium in the wall is disturbed (by earth tremors or roof collapse). This process of decay can be halted by refilling the hollow wall cores with cement, as was done for the Barracks perimeter walls in 1977.

Doorway and Window Treatment

Because doorways and windows act as weakening interruptions in the structure of the wall, much greater attention was paid to the quality of frame construction. The result is that frequently doorways and windows have remained after the walls had collapsed around them. This was because carefully dressed blocks were used for lintels and doorposts, which made the joints between the stones extremely tight and able to withstand much greater vertical force than the plaster-filled joints of the walls.

Rough Wall Finish

Because of its hardness, basalt is difficult to dress to a smooth finish. Although excellent carving and dressing of basalt is evident in wealthier cities like Umm Qais and Bosra, the townspeople of Umm el-Jimal could not afford the cost of achieving such finesse and avoided working the basalt more than necessary. Hence, most walls are constructed of small building blocks with fairly rough faces.

It must be remembered that the buildings were plastered and painted both inside and out, and that the somber effect created by the greyblack color of the stone today is not typical of how the city appeared in antiquity.