The name comes from the Latin nemus, the sacred wood. In antiquity there was no town here: there was the grove, and in the grove one of the most famous sanctuaries of the Roman world, the temple of Diana Nemorensis, on the northern shore of the lake, beneath the cliffs where the village now stands. To build it the northern end of the lake had to be drained, and for that, probably in the republican age, an emissary was cut through the rock: a tunnel a little over a kilometre and a half long, five and a half metres high at its mouth, which comes out in the next valley; in later centuries it also worked a mill. The lake, though, does not belong to the comune: the water is the province's, and Nemi owns only the shores that run around it. Below the old centre they place the spring of the nymph Egeria, who, inconsolable at the death of Numa Pompilius, withdrew into Diana's wood and was there turned into water.
Caligula had two enormous ships built for this lake, one a floating shrine and the other a pleasure boat with buildings on it; after his fall they were sunk. In the Renaissance Leon Battista Alberti tried to raise them by roping them to floating barrels, and failed, because the wood had rotted. They were recovered between the late twenties and 1932, by lowering the level of the lake through the ancient Roman tunnel, and put in a museum built for them on the shore. On the thirty-first of May 1944 the museum burned and the ships were destroyed. The rest of Nemi's story is smaller and more stubborn: in 1482 Sixtus IV granted the fief to the men of Velletri for their conduct in war, the grant did not last, and the quarrel over the boundary had to be settled twice, in 1505 and in 1546. In 1514 a Colonna gave the village its statutes. Today Nemi is the second smallest comune of the Castelli Romani and is known for its strawberries, which have their feast on the first Sunday of June.