ORSINI, the name of a Roman princely family of great anti quity. According to tradition the popes Paul I. (757) and Eu genius II. (824) were of the Orsini family, but the probable founder of the house was a certain Ursus (the Bear), about whom very little is known, and the first authentic Orsini pope was Giacinto Orsini, son of Petrus Bobo, who assumed the name of Celestin III. (1 i9i). The latter endowed his nephews with church lands and founded the fortunes of the family, which alone of the Guelph houses was able to confront the Ghibelline Colonna. "Orsini for the church" was their war-cry in opposition to "Co lonna for the people." In the 13th century the "Sons of the Bear" were already powerful and rich, and under Innocent III. they waged incessant war against other families, including that of the pope himself (Conti). In 1241 Matteo Orsini was elected senator of Rome, and sided with Pope Gregory IX. against the Colonna and the Emperor Frederick IL, saving Rome for the Guelphic cause. In 1266 the family acquired Marino, and in 1277 Giovanni Orsini was elected pope as Nicholas III.
When Boniface VIII. proclaimed a crusade against the Colonna in 1297, the Orsini played a conspicuous part in the expedition and captured Nepi, which the pope granted them as a fief. On the death of Benedict XI. (1304) fierce civil warfare broke out in Rome and the Campagna for the election of his successor, and Cardinal Napoleone Orsini appears as the leader of the French faction at the conclave. The Campagna was laid waste by the feuds of the Orsini, the Colonna and the Caetani. At this time
the Orsini held the castle of S. Angelo, and a number of palaces on the Monte Giordano, which formed a fortified and walled quar ter. In 1332, during the absence of the popes at Avignon, the feuds between Orsini and Colonna, in which even Giovanni Orsini, although cardinal legate, took part, reduced Rome to a state of complete anarchy. The Orsini were again at war with the Co lonna at the time of Rienzi. In 1435 Francesco Orsini was ap pointed prefect of Rome, and created duke of Gravina by Pope Eugenius IV. In 1484 war between the Orsini and the Colonna broke out once more, the former supporting the pope (Sixtus IV.). Virginio Orsini led his faction against the rival house's strongholds, which were stormed, the Colonna being defeated.
The Orsini fortunes waxed and waned many times, and their property was often confiscated, but they always remained a pow erful family and gave many soldiers, statesmen and prelates to the church. The title of prince of Solofra was conferred on them in 5620, and that of prince of the Holy Roman empire in 1629. In 1724 Vincenzo Maria Orsini was elected pope (Benedict XIII.) and gave his family the title of Roman princes.
See F. Sansovino, Storia di casa Orsina (Venice, 1565) ; F. Gregoro vius, Geschichte der Stadt Rom (Stuttgart, 1872) ; A. von Reumont, Geschichte der Stadt Rom (1868) ; Almanach de Gotha.