ABSTRACT
A clearly Eastern element, possibly of Byzantine origin, is the technique of flooding a moat with water in order to strengthen the defences of fortifications erected in flat terrain, such as is the case at Calatrava la Vieja, in the province of Ciudad Real (Retuerce and Zozaya, forthcoming). Here a series of large hydraulically propelled waterwheels transported water up from the River Guadiana to the top of the fortress parapet, from whence it flowed into a tower or "castellum acquae". This tower had a pressure-regulating system that permitted excess water to be used to flood the nearby moat.
