The ancient architectural remains at the site date mostly from the Republican period. These include a circuit of fortification walls built using polygonal masonry. The walls incorporated a system of gates, including the Porta Saracena which is covered by a large monolithic architrave. Atop the ancient acropolis of Segni sits the podium of the temple of Juno Moneta, which now supports a Medieval church of Saint Peter (tenth century).
On several occasions Segni served as a place of refuge for popes, and the mid-twelfth century Eugene III erected a palace there. In the twelfth century it came into possession of the Counts of Marsi, hereditary enemies of the Orsini. The family called de' Conti produced several popes (Innocent III, Gregory IX and Alexander IV) and many cardinals. In 1558 Segni was sacked by the forces of the Duke of Alba in the war against Pope Paul IV; immense booty was captured, as the inhabitants of the other towns of the Campagna had fled thither. Politician Giulio Andreotti was born in Segni in 1919.
- Co-cathedral of Santa Maria Assunta, built in the early 17th century on the former temple of St. Bruno. The bell tower is from the 11th century. The interior has a painting by Francesco Cozza.
- Polygonal walls.
- Ancient acropolis
- Mycenae, Greece
- G.M. De Rossi Segni (1982).
- Francesco Maria Cifarelli Il tempio di Giunone Moneta sull'acropoli di Segni: storia, topografia e decorazione architettonica (2003).
- Quilici, L., S. Quilici Gigli, R. Talbert, T. Elliott, S. Gillies. "Places: 423072 (Signia)". Pleiades. Retrieved March 8, 2012.