Pula, S Maria Formosa
|location is wrong
Bishop Maximian of Ravenna (of S Vitale fame) used mosaic in the church (now the church of S Maria Formosa) he built in Pula, just across the Adriatic from Ravenna. Pula in the Roman province of Istria was an important bishopric in the fifth and sixth centuries; more importantly, Maximian himself was from Pula and had been a deacon in the church there. A fragment of his mosaic – part of a beardless Christ with a white-bearded man to his right – St Peter perhaps - survives. Though I haven't seen it yet.