The Romans chose the location of aqueducts in some of the most important cities of the Empire. We focus in particular on the city of Nîmes, ancient Nemausus, and the magnificent challenge of providing it with one of the most spectacular water supplies of antiquity. It shows through precise and elaborate computer simulations, the works and engineering necessary to make it come true: the techniques that the Romans used to pierce the mountains, save the valleys and gorges and distribute the water to the city.