The Nymphaeum of the Tritons, so-called because of the presence of reliefs of these figures in the act of sounding sea horns, is one of the two large monumental fountains of the city. The 60 metre long façade has two short wings that house niches for statues. Remains of the marble trabeation (horizontal beams or lintels which are borne up by columns or posts, as opposed to an arched construction) of the lower order are preserved. The back wall of the nymphaeum has collapsed because of earthquakes. Systematic excavations have brought to light the fragments of figured and architectural decoration in marble which had collapsed into the large basin that opened to the street: slabs with scenes of the Amazonomachy and personifications of rivers and springs, pediments with Tritons, dolphins and Erotes riding fish. The Nymphaeum was built during the reign of Alexander Severus (AD 222 – 235), as the inscription on the architrave blocks attest.

One sees it to the left after having passed the Byzantine Gate at the north of the Colonnaded Street, that we see on some of the pictures.