The true origin of the name had already been forgotten, and Cassiodorus supposes that "Virgo's stream is so pure that the name, according to common opinion, is derived from the fact that those waters are never sullied, since, while all the others give evidence of the violence of rainstorms by the turgidity of their waters, Virgo alone ever maintains her purity." It was quite a natural supposition, for the Virgo Water has never had a filtering or settling reservoir. Those who have the good fortune to drink it receive it from its Roman fountains exactly as it comes from its springs on the Via Collatina. This aqueduct was cut off from the city in 537 by the Goths and Burgundians, and, though in the same year Belisarius restored the aqueducts of Claudius and Trajan, the Virgo seems to have remained entirely unused for the next two hundred years. During that period the popes were not sufficiently powerful to undertake any great public works, but when Charlemagne visited Rome in 778 he gave the needed support to the head of the church, and thereafter the popes began the restoration and the maintenance of the Roman aque­ducts. The Virgo was restored in 1447 by Nicholas V, in whose pontificate Constantinople was taken by the

Turks and the Wars of the Roses began in England. He was a great Pope and repaired the aqueduct so thoroughly that it remained in use for thirty years. There must always have been a main fountain for the Virgo Water, but the records of the modern "Fountain of Trevi" begins with the fountain which Vasari says was rebuilt by Nicholas V's architect, Leon Batista Alberti. After a short period the aqueduct was again restored and the fountain enlarged by "The Great Builder," Sixtus IV. Then occurs a period of various vicissitudes, and finally, in 1670, Pius V restored the Virgo Aqueduct effectively and rebuilt Sixtus IV's fountain, making what is now known as the "old Trevi fountain." This fountain stood not where the present one stands, but to the west of it, in the little Piazza Santa Crocifere. The old engravings show it to have been a huge semicircular pool into which the water poured from three great apertures made in massive stone piers.

The name of Trevi is supposed by some writers to be derived from these three streams of water-three ways, Trevii; but there is more reason to believe that the fountain took its name from the mediaeval name of that quarter of the city - Regione Trevi, from trevium, because of three roads which converge near the present Piazza of Trevi.