Technology
The ancient Romans also had a complex system of aqueducts, which were used to transport water across long distances. The first Roman aqueduct was built in 312 BCE. The eleventh and final ancient Roman aqueduct was built in 226 CE. Put together, the Roman aqueducts extended over 450 kilometers, but less than seventy kilometers of this was above ground and supported by arches.
Cura Annonae
A steady supply of water was needed for watermills and this came from the Aqua Traiana, an aqueduct bringing water some from springs near Lake Bracciano to Janiculum hill just outside the walls of the city of Rome. The aqueduct was inaugurated in 109 CE and the water it carried was used initially as drinking and bathing water. A famine (and resultant riots) in 190 CE caused by corruption in the grain distribution system influenced the Roman government under Emperor Septimus Severus to intervene and convert the distribution of grain to the populace into the distribution of flour. The watermills constructed at Janiculum "were intended to centralize, regularize, and perhaps even deprivatize the city's milling operations." Estimates of the date when the watermills came into operation vary, but it was probably in the early 3rd century.