Lake Nemi fills a small volcanic crater in the Alban Hills a short distance southeast of Rome, its still, round basin giving it the poetic name Ovid uses in the Fasti, speculum Dianae, "Diana's mirror." On its northern shore stood one of central Italy's most important sanctuaries to Diana, worshipped there specifically as Diana Nemorensis, "Diana of the Wood," a cult that predates Roman control of the site and drew worshippers, including a documented Roman aristocratic dedication by a consul in the fourth century BCE, from well beyond the immediate area. The sanctuary combined worship of Diana as huntress and protector of wild places with cults of Egeria, a water nymph associated in Roman legend with king Numa Pompilius, and of Virbius, a minor woodland deity later mythographers identified with the Greek hero Hippolytus, reborn after his death and hidden in Diana's grove.
Archaeological excavation of the sanctuary site, carried out from the nineteenth century onward, has recovered a substantial body of votive offerings, statuary and architectural remains confirming the site's importance across several centuries of use, extending from the pre-Roman period through the Roman imperial era. The lake's own physical isolation, ringed by wooded hills with no natural outlet visible at the surface, likely reinforced its reputation as an especially numinous and enclosed sacred landscape distinct from more urban Roman cult sites.