Early Aquedusts

For most of their length the early aqueducts were simply channels bored through the rock, from the water lakes in the hills to the cities in Rome. The depth of the channel below ground varied so as to maintain a constant, very shallow gradient (less than 1/200) throughout the length of the aqueduct; vertical shafts were bored at intervals to provide ventilation and access. Only in the final stretches was the conduit raised on arches, to give a sufficient head for distribution of the water within the city.