The Tempio di Diana Nemorense(Temple of Diana in Nemi) located on the banks of the lake increasingly gained importance as a place of worship for the Latin League and remained such even under Roman rule. The Romans embraced the religious cult inasmuch as Emperor Caligula organized magnificent celebrations in honour of Diana aboard his ships, which were anchored in the centre of the small volcanic lake.
The two big vessels were recovered from the bottom of the lake in the 30s and conserved in the Museo delle Navi Romane (Museum of the Roman Ships) until the Germans set fire to the museum and destroyed them during the Second World War.
In Medieval times a flourishing agricultural community, so-called Massa Nemus, developed around Lake Nemi producing mainly fruit and wine. However, Emperor Constantine the Great entrusted it to the Basilica of Giovanni Battista in Albano to increase the power of the church.
Around the 9th century, the Castle was built (the Castrum Nemorensis) and Nemi fell once more under the rule of the Counts of Tusculum. The Frangipane family replaced them around the year 1090. However, in 1153, Pope Anastasius IV assigned the castle to the Trappist Monks belonging to the Abbey of the Three Fountains in via Laurentina. Under this rule, Nemi acquired its present layout and underwent a peaceful period, also due to its well-protected position.
At the beginning of the 15th century, as a reward for his support during the crusade against the Caetani and Colonna families, Pope Boniface IX handed Nemi over to Teobaldo Annibaldi. Riccardo Annibaldi returned it to the Trappist monks for a short period in 1412 and the Colonna family then purchased it in 1428.
In 1479, the Colonna family sold the fiefs of Nemi and Genzano di Roma, as a collateral guarantee, to Cardinal Guillaume d’Estouteville who, in 1983, handed them over to his natural sons Agostino and Girolamo that he had with Girolama Tosti.
Pope Alexander VI in 1501 – with the papal brief Coelestis altitudine potentia – granted his nephews Giovanni and Rodrigo Borgia several fiefs including Nemi. However, due to their young age, the territories were governed by Cardinal Bishop of Cosenza Francesco Borgia. After the Pope’s death, the land was returned to the Colonna family but, at a later stage were taken over by a number of families: Cesarini (1550), Piccolomini (1560), Cenci (1563), Frangipane (1572), Braschi (1782) and eventually the Orsini family (1860).
Once Italy was united, Nemi became a Comune, even though the castle and the surrounding properties were bought by the Ruspoli family who not only renovated the ancient building, but also took care of the town’s much-needed public works.
Between the 19th and 20th centuries, Nemi became an important stopover of the Grand Tour, because of its picturesque view, which attracted renown visitors such as Barthold Georg Nieburg, Charles Gounod, Charles Didier, Massimo D’Azeglio and James Frazer.