Structures known as ___________ were built with a solid core of sun-dried mud-brick and given an external facing of weather-proof baked bricks. The mud-bricks of the core were separated every few courses by a layer of reeds and matting that reinforced and bound together the great mass of brick. In some cases thick woven ropes, 100 mm in diameter, provided further reinforcement. Horizontal ‘weeper holes’ ventilated the core, thus reducing humidity and stabilizing the mud-brick, and vertical shafts through the brickwork provided drainage. In many such structures the central core seems to have been fired, but whether this was done deliberately or whether these structures were in some way self-igniting is not clear.