"This was an extraordinary monument, a vaulted, three-chambered semicircular nymphaeum (a monument consecrated to the nymphs in ancient Greece and Rome). At the center there was a small temple dedicated the spring god, while on both sides there were two basins," Quilici said.
Roofed with quite extraordinary vaults, still decorated with Egyptian blue, the basins filtered the spring water through bricks laid with gaps between them.
"The basins had two functions: they collected the waters for the aqueduct and provided quite beautiful scenery," Quilici said.
According to the researchers, the richly decorated vaulted ceilings suggest that Trajan (the 13th Roman emperor) almost certainly came there for the aqueduct's inauguration.
Indeed, the emperor may have been in that area on June 24, 109 A.D., according to historical records.
"By coincidence we first explored the aqueduct on June 24, 2009, exactly 1,900 years later," O'Neill pointed out.
Trajan commemorated the opening of the aqueduct by minting a Roman coin and building a fountain on Janiculum Hill, right where the waters entered the city.