Originally a Nymphaeum was the monument at the head of a sacred spring, where votive offerings could be made to the nymphs, guardians of the water, these having replaced the natural sacred grottos and caves from which water issued.
Gradually the nymphaeum changed from their having solely ritual use, to also being a decorative fountain, supplying water, and also a cool refreshing area for meeting within the cities, which due to its association with water was often used for wedding services.
The base of the reservoirs were often covered in mosaics, and theirs was the first application of the mosaics continuing up the walls from the floor.
The fountain at Jerash, dedicated to the nymphs, was built in 191 CE from marble, with a half domed roof and coloured plasterwork, adorned with statues. The water flowed from the mouths of seven carved lion heads into basins, and overflowed into the drains beneath the street.
Whilst many nymphaeums are built to this semi circular pattern, as symbolic representations of grottos, most were built as circular rotundas, similar to the smaller modern fountains.
Near the Mithraeum at Carrawburgh on Hadrian's Wall, a nymphaeum was discovered in 1876 which was dedicated to the British water Goddess Coventina, however its location has since been lost.