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How a Roman Aqueduct Works - Archaeology Magazine Archive:
Ancient aqueducts were essentially man-made streams conducting water downhill from the natural sources to the destination. To tap water from a river, often a dam and reservoir were constructed to create an intake for the aqueduct that would not run dry during periods of low water. To capture water from springs, catch basins or springhouses could be built at the points where the water issued from the ground or just below them, connected by short feeder tunnels. Having flowed or filtered into the springhouse from uphill, the water then entered the aqueduct conduit. Scattered springs would require several branch conduits feeding into a main channel.