The aqueduct at Nimes, in southern France (Pont du Gard)

These aqueducts were quite a challenge to build. The engineering had to be just right in order to get the water to run through the channels and get to the city without stagnating in the channel or coming too fast into the city. They had to keep the slope the same all the time, so sometimes the aqueducts had to run on high arches, and other times along the ground in stone channels, or even under the ground in tunnels.