Ave Roma Immortails, Volume 1 by F. Marion Crawford

In Imperial times, the street now called the Tritone, from the Triton on the fountain in Piazza Barberini, led up from the Portico of Vipsanius Agrippa's sister in the modern Corso to the temple of Flora at the beginning of the Quattro Fontane. It was met at right angles by a long street leading straight from the Forum of Trajan, and which struck it close to the Arch of Claudius. Then, as now, this point was the meeting of two principal thoroughfares, and it was called Trivium, or the 'crossroads. ' Trivium turned itself into the Italian 'Trevi,' called in some chronicles 'the Cross of Trevi. ' The Arch of Claudius carried the Aqua Virgo, still officially called the Acqua Vergine, across the highway; the water, itself, came to be called the water 'of the crossroads' or 'of Trevi,' and 'Trevi' gave its name at last to the Region, long before the splendid fountain was built in the early part of the last century.

The device of the Region seems to have nothing to do with the water, except, perhaps, that the idea of a triplicity is preserved in the three horizontally disposed rapiers.