While probably there was never any break in the communication between the churches of the East and those of the West, it is likely that they developed their liturgical forms more or less independently until about the middle of the fourth century. Then the floodgates of Oriental influence seem to have been opened by St. Hilarius and St. Ambrose. The former, who was bishop of Poitiers, is said to have introduced into his church the antiphonal and other forms of psalmody then practised in the churches of Asia, where he had lived in exile for four years (356-60). He is supposed to have introduced the Syrian hymnody into the Western Church. '_Hymnorum carmine floruit primus_,’ Isidor of Seville said of him. He is credited with having been the pioneer of the metrical style of hymn known as Ambrosian, though the three hymns from his pen which have been preserved hardly bear out this contention. They are crude in rhythm and not likely to have served as models for the cultured Ambrose. From all available evidence one is impelled to award to St. Ambrose the honor of having first introduced antiphonal psalmody to the West.[56] Indeed there is little doubt that he was the real founder of the Latin chant in general. Ecclesiastical songs, as we have already seen, had already developed, both in the East and in the West, to something like a formal art; but Ambrose seems to have been the first to gather together the various elements composing it and lay the foundations of a strictly ordered liturgy. From Milan the antiphonal psalmody spread through all the churches of the West. Even Rome, which until the twelfth century excluded the Ambrosian hymns, adopted antiphonal psalmody in the time of Pope Celestine I (422-32).[57] It is to Rome that one must look for the subsequent development of liturgical song; though until the time of the great schism the formative influences were more Byzantine than Latin. St. Leo the Great (440-61) established in the immediate vicinity of the Basilica of St. Peter a monastic community especially entrusted with the service of the canonical hours, under the patronage of Saints John and Paul, and this was followed in the second half of the seventh century by the community of St. Martin and, under Gregory III (731-41), by that of St. Stephen. IV