Water Flow in the Castellum at Nîmes

The characteristics of water flow in the unique Roman castellum at Nîmes are investigated from the perspective of modern hydraulics. The study comprises normal operations, when the water flowed into the distribution pipes, as well as drainage for maintenance, when the water escaped through the floor drains. The enigmatic gate mechanism at the entrance, which affected each of these operations, is the main focus of the investigation. The conclusions are that 1) the distribution pipes as well as the aqueduct channel were designed for maximum effectiveness at the probable flow rates; 2) appearances to the contrary, the drain openings were rationally proportioned; 3) an adjustable gate mechanism, such as the archaeological evidence suggests, would not have been a complex redundancy, but an essential feature of a first-rate distribution basin: the device was needed not only to measure water flow, but also to facilitate drainage; and 4) as a water meter, the gate would have functioned best by measuring the flow through a submerged orifice, using the orifice size as the parameter.