The Aqua Traiana (Trajan Aqueduct) in Rome was built by the Emperor Trajan and was inaugurated on June 24th of the year 109 AD. It is more than 32km (just over 20 miles) long.
Trajan Aqueduct Rome
History and description
The source of the Trajan Aqueduct is near the Lake of Bracciano. It entered Rome at the Porta San Pancrazio (near the Janiculum Hill). The aqueduct was meant to bring water to the mills of Trastevere.
In 537 the Ostrogoths destroyed part of the aqueduct and the mills were left without water. In the beginning of the 17th century, Pope Paul V Borghese managed to restore and reopen the aqueduct, a.o. by building an arch made of Travertine marble over the Via Aurelia.
The marble arch became known as the Arco di Tiradiavoli (“Arch of the Devilthrowers”), for a stretch of road which was known as the Via di Tiradiavoli.
There is an inscription on the arch saying it was built by the Emperor Augustus. Apparently the Pope thought (mistakenly) that it was the Aqua Alsietina he was restoring instead of the Aqua Traiana.

After the restoration the aqueduct came to be called the Aqua Paola Aqueduct, just as the monumental fountain at its end came known as the Fontana dell’Acqua Paola.
The enterprise turned out to be incredibly expensive and a special tax was created, first on meat and later also on wine.
Between 1673 and 1696 water from the Lake of Bracciano itself became one of the aqueduct’s sources, but its quality as drinking water left much to be desired. From then on Romans started referring to worthless objects as “being as valuable as the “Paola Aqueduct“.