The workforce itself was of a stupendous size. Thousands of architects and engineers, legal experts, surveyors and carpenters, blacksmiths, diggers and ordinary labourers were recruited from across the Abbasid empire. First they surveyed, measured and excavated the foundations. Then, using the sun-baked and kiln-fired bricks that had always been the main building material on the river-flooded Mesopotamian plains in the absence of stone quarries, they raised the fortress-like city walls brick by brick. This was by far the greatest construction project in the Islamic world: Yaqubi reckoned there were 100,000 workers involved.
