Rome, Capitoline Hill, Via di San Pietro in Carcere, Aqua Marcia fountain east of the Palazzo Senatorio.

S P Q R / ACQVA MARCIA - inscription on an Aqua Marcia fountain east of the Palazzo Senatorio, Rome, Capitoline Hill, Via di San Pietro in Carcere.

The Aqua Marcia was constructed from 144–140 BC by the praetor Quintus Marcius Rex (an ancestor of Julius Caesar), for whom it is named. It followed the via Tiburtina into Rome, and entered the city in its eastern boundary at the Porta Tiburtina of the Aurelian Wall. The aqueduct was well known for its cold and pure waters.

The aqueduct was largely paid for by spoils from the recent Roman conquests of Corinth in 146 BC and the destruction of Carthage at the end of the Third Punic War, in the same year. The water provided by the Aqua Marcia was an important ingredient allowing Rome's expansion into a large imperial city.

The ancient source for the aqueduct was near the modern towns of Arsoli and Agosta, over 91 km away in the Anio valley. This general locale, in hills to the east of the city, was used for other aqueducts as well, including the Anio Vetus, Anio Novus, and Aqua Claudia. The same source is used today to supply the modern aqueduct.

The Aqua Marcia supplied water to the Viminal Hill in the north of Rome, and from there to the Caelian, Aventine, Palatine, and Capitoline regions of the city. Its extension to the Capitoline Hill caused a controversy at the time, because traditionalists were concerned about a passage in the Sibylline Books warning against bringing water there.

The aqueduct was repaired by Marcus Agrippa in 33 BC, and then later again by Augustus, according to the inscription in the arch that was later made into the Porta Tiburtina. Augustus also augmented the supply by linking it to an additional source, the Aqua Augusta, doubling the throughput. Much of its supply was siphoned off by private citizens for their own use, making it effectively only a trickle in the city by the time of Nero. The supply was increased again by later emperors. By the time Frontinus measured the city's aqueducts around 97, the Aqua Marcia was capable of supplying 187,600,000 l (49,600,000 US gal; 41,300,000 imp gal) of water a day, the second-greatest source of the city's water.

more on https://en.wikipedia.org/wiki/Aqua_Marcia

picture generously provided by Rudolf Kaufmann (2015)