This public nymphaeum is the monumental facade of a water reservoir. The structure was built in opus latericium and belongs to the Hadrianic period. It probably supplied the fountains in the nearby Case a Giardino (Garden Houses).

The reservoir consists of two lower and two upper rooms. The lower rooms have barrel vaults. They could contain 26.000 liters. The upper rooms were probably fed by a branch of the aqueduct, that was supported by the republican city wall. These rooms could contain 21.750 liters. On either side of the reservoir is a service area. The nymphaeum has three niches, a semicircular niche in the centre, and two rectangular niches on either side. In front of the niches is a basin.