The Aqua Marcia (Italian: Acqua Marcia) was one of the longest of the 11 aqueducts that supplied the city of ancient Rome. The aqueduct was built between 144–140 BC, during the Roman Republic. The still-functioning Acqua Felice from 1586 runs on long stretches along the route of the Aqua Marcia.
The ancient source for the aqueduct was near the modern towns of Arsoli and Agosta, over 91 km (57 mi) away in the Anio valley. This general locale, in hills to the east of the city, was also used for other aqueducts 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. Frontinus measured the flow of the Aqua Marcia at its source around AD 97 as 4690 quinariae, making it the second-greatest source of the city's water. Modern estimates of size of one quinaria vary over a wide range, from 10,000 l (2,600 US gal; 2,200 imp gal) to 76,800 l (20,300 US gal; 16,900 imp gal) of water a day, giving the Aqua Marcia a flow rate of 46,900,000 l (12,400,000 US gal; 10,300,000 imp gal) to 360,192,000 l (95,153,000 US gal; 79,231,000 imp gal) of water a day.
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