Formosus 1 was bishop of Portus ("Formosum Portuensem" sc. episcopum); he and the bishop of Populonia, Paulus (Paulos 57), were chosen by the bishop of Rome, Nicholas I (Nikolaos 28), to go to Bulgaria in 866 and preach to the people there, following a request from the Bulgar king Michael (Boris 1): 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 on the journey by Donatos 2, Leo 164 and Marinos 15, who continued en route to Constantinople while Paulos 57 and Formosus 1 remained in Bulgaria: Lib. Pont. 107. 70-71. There they preached and baptised and familiarised the Bulgars with the rites of the Christian faith; the Bulgar king expelled all missionaries of other nationalities ("alienigenas") and allowed only the representatives from Rome to preach; he then asked for Formosus 1 (here described as "vita et moribus episcopum") to be consecrated as archbishop for him: Lib. Pont. 107. 73. Nikolaos 28 replied that Formosus 1 could not be spared from his existing flock and sent a number of priests from whose number a suitable candidate was to be chosen: Lib. Pont. 107. 74. The pope intended Formosus 1 to leave Bulgaria and proceed to Constantinople accompanied by the bishop of Trevi, Dominikos 3, in connection with the affair of the patriarchs Photios 1 and Ignatios 1, but before this could happen the emperor Michael (Michael 11) died and was replaced by Basil (Basilios 7), and Photios 1 was dismissed as patriarch and replaced by Ignatios 1: Lib. Pont. 107. 75-76.

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