Segni (Latin: Signia, Ancient Greek: Σιγνία) is an Italian town and comune located in Lazio.

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).

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.