Orsini (ōrsē´nē), powerful Roman family that included three popes and numerous other churchmen, soldiers and statesmen. The eponymous ancestor was one Ursus. Giacinto Orsini, who became Pope Celestine III in 1191, founded the family's greatness. Matteo Rosso Orsini was elected a Roman senator in 1241, and in 1277 Giovanni Gaetano Orsini ascended the papal throne as Nicholas III. The long rivalry between the Guelph Orsini family (see Guelphs and Ghibellines) and the Ghibelline Colonna family lasted until the early 16th cent. and often plunged Rome into anarchy. The Orsini were made princes of the Holy Roman Empire in the 17th cent. Among the prominent members of the family were Lorenzo Orsini (d. 1536), who defended (1527) Rome and the Castel Sant' Angelo against the troops of Holy Roman Emperor Charles V; the princesse des Ursins; and Pietro Francesco Orsini, who became Pope Benedict XIII in 1724. Representatives of the family are still living.