Paulos 57 was bishop of Populonia ("Paulum Populoniensem episcopum", or similar): Lib. Pont. 107. 57, 69, 75. He was sent to Sardinia by the bishop of Rome, Nicolas I (Nikolaos 28), together with the abbot Saxu 1, to repress the custom of incestuous marriages; they excommunicated and anathematised those who refused to obey and after a vigorous campaign of preaching returned to Rome: Lib. Pont. 107. 57. Following a request to the bishop of Rome from the ruler of Bulgaria, Michael (Boris 1), in August 866, for help in converting his people to Christianity, Nikolaos 28 appointed Paulos 57 and the bishop of Portus, Formosos 1, as his representatives ("sedis apostolicae missos"), to go to the Bulgars and preach to the people: Lib. Pont. 107. 69. They are the unnamed western bishops who tried to introduce the Latin rites into Bulgaria in c. 866; in a letter to the eastern patriarchs Photius (Photios 1) complained about their activities: Photius, Ep. 2, lines 56ff., 81 (I 42 Laourdas-Westerink). They were accompanied by the bishop of Ostia, Donatus (Donatos 2), the priest Leo 164 and the deacon Marinus (Marinos 15), who proceeded onwards through Bulgar territory to Constantinople, while Paulos 57 and Formosos 1 remained in Bulgaria: Lib. Pont. 107. 70-71. They were welcomed by the Bulgar king and began to preach and to baptise; the king meanwhile expelled from his kingdom all preachers of other nationalities ("omnes a suo regno pellens alienigenas") and only the missi of the bishop of Rome were allowed to preach: Lib. Pont. 107. 73. When Boris 1 asked for an archbishop to be appointed, Nikolaos 28 ordered a new mission to go to make arrangements and told Paulos 57 to remain preaching in Bulgaria with a member of the new mission, the bishop of Polimartium, Grimoald 5, while other members of the mission proceeded to Constantinople: Lib. Pont. 107. 75.

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