Segni (in Latin Signinsis) is an Italian hill town located in the Province of Rome. Situated on a hill in the Lepini Mountains , Segni overlooks the valley of the river Sacco . There still exists the double enclosure of a cyclopean wall and the gates, including the Porta Saracinesca the "Saracen Gate", with a large monolithic architrave. There are also the ruins of a church dedicated to Saint Peter and some underground excavations, which recall Etruscan influence. The King of Rome Lucius Tarquinius Superbus brought Siginsis under Roman control. With other cities of Latium it rebelled against Rome more than once.

On several occasions Segni served as a place of refuge for popes, and Eugenius 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.

Bishops of Segni. The legendary founding bishop of Segni was remembered only as Sanctulus (the "little saint"), about 494; among his successors are: Saint Bruno of Segni (1079), who wrote a commentary on the New Testament and a [pamphlet against simony]; Trasmundo (1123), deposed for supporting the Antipope Anacletus II, but restored after he switched allegiances; under Pope John III (1138), Thomas a Becket was canonized in the cathedral (1173); Lucio Fazini (1482), renowned for his erudition; Fra Bernardino Callini (1541), wrote the life of Saint Bruno; Giuseppe Panfili , O.S.A. (1570), later deposed and imprisoned; Paolo Ciotti (1784), who governed the diocese during the French Revolution. The diocese of Segni is directly subject to the see of Rome.