A serious logistical problem faced by the authorities in Rome was the water supply. As the empire grew, and Rome became richer, it naturally attracted more people and they all needed water. The Tiber was the drain so that was not available and so the answer the Romans came up with was the aqueduct. In the end there were 11 acquedotti supplying the city with an extravagant 300 million gallons of water per day and every one was gravity fed. The longest was over 90 kilometres long and for the most part they ran underground, following the contours of the hills. However, as they approached the city this was no longer possible and so they were raised up on arches. If you go just south of the city, in the general direction of Ciampino airport, you can see the spectacular remains of three of these engineering wonders.
The oldest and the least impressive – in terms of the height of its arches – is the Aqua Marcia built between 144 and 140 BC. It was paid for in large part by the proceeds of the sack of Corinth and the destruction of Carthage and is the longest of all at over 91 kilometres.
Close by is the impressive series of arches, some over 100 feet high, that carry the Aqua Claudia. Standing next to them allows you to fully appreciate the skill of the engineers and architects who designed and built them. But construction of this magnitude was expensive, even for a city as rich as Rome, and so being pragmatists they put another aqueduct above the channel for the Aqua Claudia and thus brought the water for the Aqua Anio Novus into the city. Both these projects were started under the reign of Caligula, who is mainly known for being a sadistic pervert but clearly there was another side to his character. They were completed under his successor Claudius, around 52AD.