Noble Roman family of Jewish origin. A Jewish banker of Rome who had acquired a princely fortune was baptized in the first half of the eleventh century, took the name of Benedictus Christianus, and married the daughter of a Roman nobleman. Leo, the offspring of this union, and one of the most powerful magnates of the city, had a castle in Trastevere and affiliated himself with the papal party, and his son Petrus Leonis, from whom the family derives its name, continued his father's policy, controlling the Isola Tiberina in addition to the castle in Trastevere, and having another castle opposite the Tiber bridge near the old theater of Marcellus, which was included in the fortifications. He was the leader of the papal party and the most faithful and powerful protector of the popes. Urban II. died in Petrus' castle, and the latter defended the cause of Paschal II. against the antipopes and the emperor. When Henry V. came to Rome Petrus Leonis was at the head of the papal legation which effected a reconciliation between the pope and the emperor, but Paschal's attempt to make the son of Petrus prefect of the city caused a riot.
Petrus was prominent in the liberation of Pope Gelasius II., and when Petrus died in 1128 his son of the same name was cardinal, and had on several occasions rendered service to the Church. In 1130 Cardinal Pierleoni was elected pope under the name of Anacletus II., while the counter party chose Innocent II. The schism lasted for eight years, until the death of Anacletus, after which the family of Pierleoni made peace with the pope, retaining its power and influence, and being distinguished by various honors. Leo and Petrus, the brother and nephew of Anacletus, were papal delegates at Sutri in 1142, and another brother, Jordan, with whom the era of senators begins, became the head of the Roman republic as Patricius in 1144, while a sister is said to have been the wife of Roger I. of Sicily. In the twelfth century Cencius Pierleoni was "scriniarius" of the Church, and in 1204 John Pierleoni, who had been appointed elector by Pope Innocent III., chose Gregory Petri Leonis Rainerii as senator. The legendwhich traces the lineage of the family of Pierleoni to the ancient Roman noble family of the Anicii is as apocryphal as the story of the descent of the Hapsburgs from the counts of Aventin, who belonged to the Pierlconi.
- Baronius, Annales Ecclesiastici, years 1111, 1115;
- Gregorovius, Gesch, der Stadt Rom im Mittelatter, iv. 349 et seq.; 391 et seq.; vols. iv. and v., passim;
- Liber Pontificalis, ed. Duchesne, ii. 303, 307, 318, 322, 336, 344, 347;
- Monumenta Germaniœ Historica, v. 472 et seq., xi. 614, xii. 711;
- Duchesne, Historiœ Francorum Scriptores, iv. 376;
- Olivieri, Il Senato di Roma. p. 185;
- Vogelstein and Rieger, Gesch. der Juden in Rom, i. 214 et seq., 218, 221 et seq.;
- Kehr, in Archivio della R. Società Romana di Storia Patria, xxiv. (1901), pp. 253 et seq.