The garden includes the ruins of the ancient settlement of Ninfa, whose name seems to derive from a classical era nymphaeum, a temple dedicated to nymphs, located on an island in the small lake; nymphs were believed to dwell in mountains and groves, by springs and rivers, and also in trees and in valleys and cool grottoes. According to Charles Quest-Ritson's book Ninfa: The Most Romantic Garden in the World, the Gardens of Ninfa's first documented evidence is from Pliny the Younger, who described a temple on the premises dedicated to water nymphs.
The village already existed in the Roman era as a small village in an agricultural area. It was perhaps founded by the Volscians at the feet of the Monti Lepini. In the Middle Ages it was a rich town on the Appian Way. In 1159, Pope Alexander III was crowned there. In 1171 the Holy Roman Emperor Frederick Barbarossa sacked and burned it, after the Pope, his enemy, had taken refuge in the town.
During the Middle Ages Ninfa had more than 150 houses, several churches, mills, bridges, two hospices, a castle and a town hall. The town was encircled by a defensive wall 1,400 metres (1,500 yd) in length with guard towers.
The castle was built in the 12th century, located near the lake, outside the city walls. Santa Maria Maggiore was the town's primary church and was most likely built from the 10th century and widened in the first half of the 12th century.
The Church of Saint John is dated around the 11th century and is now in ruins. The original structure most likely had a single nave with several lateral chapels and a semicircular apse, of which parts remain. Some traces of frescoes are still visible on the walls of the ruins.