 These served a wide array of purposes, such as irrigation, flood control, river diversion, soil-retention, or a combination of these functions.The impermeability of Roman dams was increased by the introduction of waterproof hydraulic mortar and especially "opus caementicium" in the Concrete Revolution.These materials also allowed for bigger structures to be built, like the Lake Homs Dam, possibly the largest water barrier today, and the sturdy Harbaqa Dam, both of which consist of a concrete core.