Ferentino, a town of ancient origin founded by the Ernici people, still conserves visible megalithic walls approximately two kilometres long with twelve gateways. The ancient and imposing polygonal Acropolis dominates the town.

A short distance away is the Roman Market of the Republican era, and the Knights' Palace.

Particularly beautiful is the Church of S. Maria Maggiore, an early example of Cistercian architecture (1150) in Italy, and the Romanesque Church of S. Antony Abbot which, for a time, contained the remains of Pope Celestine V whose tombstone can still be seen.