This diocese was formed from the union of two suburbicarian sees. Porto, now a wretched village, was in ancient times the chief harbour of Rome. It owes its origin to the port built by Claudius on the right of the Tiber, opposite Ostia; Trajan enlarged the basin, and in a short time there grew around it a city which soon became independent of Ostia. It was near Porto that Julius Nepos compelled Emperor Glycerius to abdicate (474). During the Gothic War the town served the Goths (537 and 549) and the Byzantines (546-52) as a base of operations against Rome. In the ninth and tenth centuries it was sacked on several occasions by the Saracens. In 849 Leo IV fortified it and established there a colony of Corsicans for the defence of the coast and the neighbouring territory; but the city continued to decay. Naturally Christianity was early established there. Several martyrs of Porto are known, including Herculanus, Hyacinthus, Martialis, Saturninus Epictetus, Maprilis and Felix. The place was also famous as the probable see of St. Hippolytus (q. v.). In 314 Gregorius was bishop. The great xenodochium, or hospice, of Pammachius was built about 370. Among the other bishops should be mentioned Donatus (date uncertain), who built the basilica of St. Eutropius; Felix, a contemporary of St. Gregory the Great; Joannes, legate to the Sixth General Council (680); Gregorius, who accompanied Pope Constantine to Constantinople (710); Gregorius II (743-61); Citonatus, present at the consecration of the antipope Constantine (767); Radoaldus, who acted contrary to his instructions on the occasion of the difficulties with Photius at Constantinople (862), and who was deposed for having prevaricated in connexion with the divorce of Lothair II of Lorraine; Formosus, who became pope (891); Benedictus (963), who consecrated the antipope Leo VIII; Gregorio (c. 991), who built the irrigation system of the territory of the diocese; Benedict VIII and Benedict IX were bishops of Porto; Mauritius (1097), sent by Paschal II to establish order in religious affairs in the Holy Land; Callistus II (1119-24), who united to the See of Porto the other suburbicarian See of Silva Candida or Santa Rufina.

Santa Rufina grew up around the basilica of the Holy Martyrs Sts. Rufina and Secunda on the Via Aurelia, fourteen miles from Rome; the basilica is said to have been begun by Julius I, and was finished by Saint Damasus. In the ninth century this town was destroyed by the Saracens, and the efforts of Leo IV and Sergius III were unable to save it from total ruin: all that remains are the remnants of the ancient basilica and a chapel. The first notice of it as an episcopal see dates from the fifth century, when its bishop Adeodatus was present at the councils held by Pope Symmachus; its bishop St. Valentinus, Vicar of Rome during the absence of Vigilius, had his hands cut off by Totila. Among its other bishops mention should be made of Tiberius (594), Ursus (680), Nicetas (710), Hildebrand (906), and Peter (1026), whose jurisdiction over the Leonine City, the Trastevere, and the Insula Tiberina (island in the Tiber) was confirmed. The residence of the bishops of Silva Candida was on the Insula Tiberina beside the church of Sts. Adalbert and Paulinus, while that of the bishops of Porto was on the same island near the church of San Giovanni. The bishops of Silva Candida, moreover, enjoyed great prerogatives in relation with the ceremonies of the basilica of St. Peter. The most famous of these prelates was Cardinal Humbertus, who accompanied Leo IX from Burgundy to Rome; he was appointed Bishop of Sicily by that pope, but, having been prevented by the Normans from landing on the island, he received the See of Silva Candida, and later was sent to Constantinople to settle the controversies aroused by Michael Cærularius. He wrote against the errors of the Greeks and against Berengarius (1051-63). The last Bishop was Mainardus. Historically, therefore, the Bishop of Porto became the second cardinal, Ostia being the first, and officiated on Mondays in the Lateran Basilica; he obtained, moreover, the other rights of the Bishop of Santa Rufina, but lost jurisdiction over the Leonine City and its environs, when they were united to the city of Rome. Among its better known cardinal-bishops are: Peter (1119), a partisan of Anacletus II; Theodevinus (1133), a German, sent on many missions to Germany and to the Holy Land; Bernardus (1159), who exerted himself to bring about peace between Adrian IV and Barbarossa; Theodinus (1177), who examined the cause of St. Thomas à Becket; Cencio Savelli (1219); Conrad (1219), a Cistercian; Romano Bonaventura (1227), who obtained the confirmation of all the rights of his see; Ottone Candido (1243), of the house of the marchesi di Monferrato, sent on several occasions as legate by Innocent IV to Frederick II; Robert Kilwardby, formerly Archbishop of Canterbury, poisoned at Viterbo (1280); Matteo da Acquasparta (1290), a former general of the Franciscans and a renowned theologian; Giovanni Minio (1302), a general of the Franciscans; Giacomo Arnaldo d'Euse (1312), who became Pope John XXII; Pietro Corsini (1374), who adhered, later, to the Western Schism; Louis, Duke of Berry, created in 1412 by John XXIII.

During the incumbency of Francesco Condulmer, Nicholas V separated the sees of Porto and Silva Candida, and gave the latter to John Kemp, Archbishop of Canterbury, at whose death (1445) the sees were reunited. Then came Guillaume d'Estouteville(1455); Rodrigo Borgia (1476), who became Pope Alexander VI; Raffæle Riaria (1508); Gian Pietro Carafa (1553), who became Pope Paul IV; Giovanni Morone (1565); Cristoforo Madruzzi (1570); Alessandro Farnese (1578); Fulvio Corneo (1580); Francesco M. Brancati (1666); Ulderico Carpegna (1675), who left a legacy to defray the expenses of quadrennial missions; Carlo Rossetti (1680); Alderano Cibo (1683); Pietro Ottoboni (1687), who became Pope Alexander VIII; Flavio Chigi (1693), who enlarged the cathedral and richly furnished it; Nicoló Acciaiuolo (1700); Vicenzo M. Orsini (1715), who became Pope Benedict XIII; Giulio della Somaglia (1818); Bartolommeo Pacca (1821). In 1826, Civitavecchia was separated from the Diocese of Viterbo and Toscanella and united with that of Porto, but in 1854, with Corneto, it was made an independent see. Mention should be made of the Cardinal Bishop of Porto Luigi, Lambruschini (1847), who restored the cathedral and the episcopal palace. From the sixteenth century, the incumbency of prelates of this see was, as a rule, of short duration, because most of the cardinal-bishops preferred the See of Ostia and Velletri, which they exchanged for their own as soon as possible. The Diocese of Cære, now Cervetri, has been united with that of Porto since the twelfth century. Cære was an ancient city, called at first Agylla, where the sanctuaries of Rome and the Vestals were hidden during the invasion of the Gauls; the Etruscan tombs scattered about its territory are important archleologically. Cervetri had bishops of its own until the eleventh century; the first was Adeodatus (499), assuming that he was not the Adeodatus who signed himself Bishop of Silva-Candida in the third synod of Pope Symmachus (501). The last known was Benedictus, referred to in 1015 and 1029. The Diocese of Porto and Santa Rufina has 18 parishes, with 4600 inhabitants.

PIAZZA, Gerarchia cardinalizia; CAPPELLETTI, Le Chiese d'Italia, I; DE ROSSI in Bullettino d'archeologia crist. (1866), 37; TOMMASSETTI in Archivio della Soc. Rom. di Storia Patria, XXIII (1900), 143; BATTANDIER, Annuaire Pontifical Catholique (Paris, 1910).

U. BENIGNI.