He separated himself from the three Arian bishops in the West, Ursacius, Valens, and Saturninus, and exhibited an accusation against the last in a synod at Beziers. But the emperor, who had information of the matter from Saturninus, sent an order to Julian, then Caesar, and surnamed afterwards the Apostate, who at that time commanded in Gaul, for St. Hilary's immediate banishment into Phrygia, together with St. Rhodanius, bishop of Toulouse. The bishops in Gaul being almost all orthodox, remained in communion with St. Hilary, and would not suffer the intrusion of any one into his see, which in his absence he continued to govern by his priests. The saint went into banishment about the middle of the year 356, with as great alacrity as another would take a journey of pleasure, and never entertained the least disquieting thought of hardships, dangers, or enemies, having a soul above both the smiles and frowns of the world, and fixed only on God. He remained in exile somewhat upwards of three years, which time he employed in composing several learned works. The principal and most esteemed of these is that _On the Trinity, against the Arians_, in twelve {144} books. In them he proves the consubstantiality of the Father, Son, and Holy Ghost. He teaches that the church is one, out of which all heresies spring; not that by this she is distinguished, as standing always one, always alone against them all, and confounding them all: whereas they by perpetual divisions tear each other in pieces, and so become the subject of her triumph.[16] He proves that Arianism cannot be the faith of Christ, because not revealed to St. Peter, upon whom the church was built and secured forever; for whose faith Christ prayed, that it might never fail; who received the keys of the kingdom of heaven, and whose judiciary sentence on earth is that of heaven:[17] all which arguments he frequently urges.[18] He proves the divinity of Christ by the miracles wrought at the sepulchres of the apostles and martyrs, and by their relics: for the devils themselves confess Christ's godhead, and roar and flee at the presence of the venerable bones of his servants,[19] which he also mentions and urges in his invective against Constantius.[20] In 358, he wrote his book _On Synods_, or _On the Faith of the Orientals_, to explain the terms and variation of the eastern Arians in their synods.