The Diocese of Porto () (Oporto) is a Latin Church diocese of the Catholic Church in Portugal. It is a suffragan of the archdiocese of Braga. Its see at Porto is in the Norte region, and the second largest city in Portugal.David M. Cheney, Catholic-hierarchy.org"Diocese of Porto (Portugal)"; retrieved: 27 December 2018'

History The diocese was probably founded in the middle of the sixth century. At the third Council of Toledo (589) the Arian bishop Argiovittus, though he condemned the Arian belief and accepted the Catholic belief, was deposed in favour of bishop Constantinus.J.-D. Mansi (ed.), Sacrorum conciliorum nova et amplissima collectio, editio novissima, Tomus nonus (09) (Florence: A. Zatta 1763), p. 989; p. 1001: Constantinus Portugalensis ecclesiae episcopus subscripsi. In 610 Bishop Argebertus assisted at the Council of Toledo, summoned by King Gundemar to sanction the metropolitan claims of Toledo.Mansi, Tomus decimus (10) (Florence: A. Zatta 1762), p. 512. Bishop Ansiulfus was present at the Sixth Council of Toledo (638),Fifty-two bishops attended. They voted thanks to King Chintila for ordering the expulsion of the Jews from Spain. Mansi, Tomus decimus (10), p. 671. Hefele, Vol. IV, pp. 460-463. and Bishop Flavius at the Tenth (656).Bishop Flavius signs last of the twenty bishops who were present. Mansi, Tomus undecimus (11), p. 43.

Bishop Froaricus was one of eight bishops who attended the provincial council of Braga (675),Mansi, Tomus undecimus (11), p. 159, where it is called the Fourth Council of Braga, not the third. and the Twelfth (681),Thirty-five bishops attended. Mansi, Tomus undecimus (11), pp. 1023-1044, at p. 1039. Thirteenth (683),Forty-eight bishops attended. Mansi, Tomus undecimus (11), pp. 1059-1082, at p. 1075. and Fifteenth (688) Mansi, Tomus XII (Florence 1766), p. 21: Froaricus Portucalensis episc. subscr. Councils of Toledo. His successor Felix appeared at the Sixteenth Council (693).Padilla, pp. 322-326. Mansi, Tomus XII, p. 84, In Canon 12, Bishop Felix is said to have been translated to the diocese of Braga, and in the subscription list he signs as a metropolitan in fifth place, as Felix in Dei nomine Bracarensis atque Portuensis sedium episcopus haec decreta synodalia a nobis edita subscr.. No other bishop is recorded under the Visigothic monarchy.

Arab occupation In 716 the Arabs began their invasion and conquest of Portugal, including Lisbon, Porto, Braga, Tuy, Lugo, and Orense. The areas were depopulated.Chronicle of Sampiro, quoted by Gams, p. 108, column 2. After the Arab invasion Justus seems to have been the first bishop (c. 882). He is only a name.Flórez, España Sagrada XXI, pp. 35-36. from the Chronicon Abeldense, España Sagrada XIII, p. 437. Gomado was probably elected in 872, when King Affonso III won back the city. The names of only four other prelates have been preserved: Froarengus (906), Da Cunha, pp, 225-226. Flórez, España Sagrada XXI, p. 38-39, places Froarengus' dates "from before 906 to 911. Hermogius (912),Da Cunha, pp. 217-218, cites a charter of King Ordonho II, dated 17 August 886, subscribed by Hermogius Portuensis episcopus. This seems to place Hermogius before Bishop Froarengus. Flórez, p. 39, places his dates from 912 to 915. Hordonius (attested in 931),Flórez, p. 40-41. and Didacus (Diego) (c. 962?).Gams, p. 109 column 1. Didacus is known only from one piece of indirect evidence, where Abbot Cesareo of S. Cecilia de Monserrato says he was consecrated in Galicia by, among others, Diego Portugalense, in the reign of King Sancho I (905-925). Perhaps his grandson, Sancho II, is meant. Flórez, p. 41.

Porto fell again into Moorish hands.

Restoration On the recovery of Porto for Christianity, which was being promoted by the Burgundian Count Henry, son-in-law of King Alfonso VI of Castile and governor of the lands from the Minho River to the banks of the Tagus, priests and prelates were being imported, especially those with connections to Cluny in Burgundy.Flórez, pp. 56-57. Hugo (Hugh) became bishop (1114-1136). He had been a Canon of the Cathedral of Compostella, and under the patronage of Bishop Diego Gelmirez, a Cluniac, he was said to have been a co-author of the Historia Compostellana.Floréz, p. 57, 68. In 1103-1104 he was sent to Rome on an embassy for the Church of Compostella, and obtained a bull granting numerous privileges, one of which was the right of the Bishop of Compostella to name Cardinals of Compostella. Hugo became a Cardinal.Floréz, p. 58. In 1109 he was Archdeacon of Compostella, but at the time of his election to the diocese of Porto and not yet ordained. He was ordained a priest on the day before Passion Sunday, and was consecrated a bishop on 23 March 1113 by Archbishop Mauricio Burdino of Braga, another Cluniac.Floréz, p. 59. As Bishop of Porto he secured from Pope Paschal II, by a bull granted on 15 August 1115, exemption of his diocese from the supervisory control of the Archbishop of Braga.Floréz, pp. 297-299. Burdinus became an antipope of the Emperor V in Rome on 8 March 1118. He greatly enlarged his diocese and the cathedral patrimony increased by the donations he secured; thus, in 1120, he received from D. Theresa jurisdiction over the City of Porto with all the rents and dues thereof.Floréz, pp. 64, 299. Bishop Hugo was present at the Council of Compostella in 1114, the Council of Sagunto in 1121 (under the presidency of Cardinal Boso, the papal Legate), and the Synod of Compostella in 1122.Thomas (da Cunha) Historia ecclesiae Lusitaniae III, p. 30.

John Peculiar was promoted to Braga (1138), his nephew, Pedro Rabaldis, succeeding at Porto. Next came D. Pedro Pitões (1145 to 1152 or 1155), D. Pedro Sénior (d. 1172), and D. Fernão Martins (d. 1185). Martinho Pires instituted a chapter and was promoted to Braga in 1189 or 1190. Martinho Rodrigues ruled from 1191 to 1235. He quarreled with the chapter over their share of the rents of the see. Later on, fresh disagreements arose in which King Sancho I intervened against the bishop, who was deprived of his goods and had to flee, but was restored by the king when Innocent III espoused the bishop's cause. Another quarrel soon arouse between prelate and king, and the bishop was imprisoned; but he escaped and fled to Rome, and in 1209 the king, feeling the approach of death, made peace with him. His successor, Pedro Salvadores, figured prominently in the questions between the clergy and King Sancho II, who refused to ecclesiastics the right of purchasing or inheriting land. Portugal fell into anarchy, in which the clergy's rights were violated and their persons outraged, though they themselves were not guiltless. Finally, Pope Innocent IV committed the reform of abuses to Afonso III, brother of Sancho II who lost his crown.

Under Bishop Julian (1247–60) the jurisdiction difficulty became aggravated. A settlement was effected at the Cortes of Leiria (1254), which the bishop refused to ratify, but he had to give way. When King Afonso III determined (1265) that all rights and properties usurped during the disorders of Sancho's reign should revert to the Crown, nearly all the bishops, including the Bishop of Porto, then D. Vicente, protested; and seven went to Rome for relief, leaving Portugal under an interdict. When the king was dying, in 1278, he promised restitution. Vicente (d. 1296) was one of the negotiators of the Concordat of 1289 and the supplementary Accord of Eleven Articles. He was succeeded by Sancho Pires, who ruled until 1300. Geraldo Domingues resigned in 1308 to act as counsellor of the King's daughter Constança, future Queen of Castile. Tredulo was bishop for two and a half years. The Minorite Frei Estêvão was succeeded in 1313 by his nephew Fernando Ramires. Both uncle and nephew quarrelled with King Denis and left the realm.

Owing to the hostility of the citizens, Bishop Gomes lived mostly outside his diocese. When Pedro Afonso became bishop in 1343, he had a quarrel over jurisdiction and, like his predecessor, departed, leaving the diocese under interdict. Six years later he returned, but again the monarch began to encroach, and it was not until 1354 that the bishop secured recognition of his rights. His successor was Afonso Pires. Egídio is probably the bishop represented in the old Chronicles as being threatened with scourging by King Pedro for having lived in sin with a citizen's wife The accusation was probably groundless, but Egídio left the city, which for twelve years had no bishop.

Other bishops were: John de Zambuja, or Estêvão; and Gil, who in 1406 sold the episcopal rights over Oporto to the Crown for an annual money payment, reduced in the reign of D. Manuel to 120 silver marks; Fernando Guerra, who in 1425 was created Archbishop of Braga; and Vasco. Antão Martins de Chaves, who succeeded Vasco in 1430, was sent by the pope to Constantinople to induce the Greek emperor to attend the Council of Basle. He succeeded, and as a reward was made cardinal. He died in 1447. Succeeding incumbents were: Durando; Gonçalves de Óbidos; Luis Pires (1454–64), a negotiator of the Concordat of 1455 and a reforming prelate; João de Azevedo (1465–1494), a benefactor of the cathedral and chapter, as was his successor Diego de Sousa, afterwards Archbishop of Braga and executor of King Manuel I. The see was then held by two brothers in succession, Diogo da Costa (1505-7) and D. Pedro da Costa (1511–39), who restored the bishop's palace and enriched the capitular revenues from his own purse; Belchior Beliago; and the Carmelite Frei Baltazar Limpo (1538–52), the fiftieth bishop. He held a diocesan synod in 1540.