Eusebius of Dorylæum, Bishop of Dorylæum in Asia Minor, was the prime mover on behalf of Catholic orthodoxy against the heresies of Nestorius and Eutyches. During the earlier part of his life he followed the profession of an advocate at Constantinople, and was already known as a layman of considerable learning when he protested publicly (423) against the erroneous doctrine of a discourse delivered by Anastasius, the syncellus, or chaplain, of Nestorius. Shortly afterwards he again bore public witness against the Nestorian heresy as to the nature of Christ, this time during a discourse by Nestorius himself, which he interrupted with the exclamation that "the eternal Word had undergone a second generation"—i.e. of a woman, according to the flesh. Much disorder followed, but Nestorius replied with arguments against the "second generation".

After the Council of Ephesus (431), at which the teaching of Nestorius had been condemned, a document attributed by general consent to Eusebius was made public, in which the doctrine of Nestorius was shown to be identical with that of Paul of Samosata. Eusebius had at some period contracted a friendship with Eutyches, founded, we may fairly conjecture, on their common opposition to Nestorian error. But when Eutyches allowed himself to be betrayed into opinions which, though directly opposed to those of Nestorius, were equally contrary to the faith of the Church, Eusebius, now Bishop of Dorylteum, was no less zealous against his former friend than he had been against their common opponent. After repeated attempts at persuasion, Eusebius brought a formal charge of false teaching against Eutyches, before Flavian, who was then (448) presiding over a synod at Constantinople. Flavian was reluctant to proceed against Eutyches, and urged Eusebius to remonstrate with him privately once more. Eusebius, however, refused, saying that he had already done all he could to convince Eutyches of his errors, and that further efforts would be useless. Eutyches was then summoned to attend, but did not do so until the summons had been three times issued; he excused his refusal to obey by asserting that he had resolved never to leave his monastery and pleading distrust of Eusebius, whom he now looked upon as his enemy. At last, however, he came, attended by a large escort of soldiers and monks. He was interrogated by Eusebius, who in the meantime had been strongly pressing his case, and who now, as he said, felt some alarm lest Eutyches should succeed in evading condemnation and retaliate upon his accuser by obtaining a decree of banishment against him. Eutyches, however, was condemned and deposed; he immediately wrote a letter to the pope, complaining of Eusebius's proceedings, which he attributed to the instigation of the devil.

In the following year (449) at Constantinople, an examination was held, by imperial authority, of the acts of the synod which had condemned Eutyches, which acts he alleged to have been falsified. Eutyches was represented by three delegates; Eusebius, who wished to withdraw but was not permitted to do so, urged that the doctrinal question should not be considered on that occasion, but should be remitted to a general council. On the assembly of the council then summoned at Ephesus (see Robber Council of Ephesus), Eusebius was forcibly excluded by the influence of Dioscurus of Alexandria, who had obtained the support of the emperor. The reading of his part in the synod at Constantinople provoked an outburst of reproaches and threats: "Away with Eusebius! Burn him! As he has divided so let him be divided!" Flavian and Eusebius were deposed and banished, and Flavian only survived for three days the physical injuries he had received in the tumultuary council. Eusebius wrote to the Emperors Valentinian and Marcian, asking for a fresh hearing; and both Eusebius and Flavian sent written appeals to Rome. The text of these appeals was discovered in 1879 by Amelli—who was then curator of the Ambrosian Library at Milan and afterwards became Abbot of Monte Cassino—and was published by him in 1882. Eusebius grounds his appeal on the fact of his having been condemned unheard, and prays the pope to quash the sentence (pronuntiate evacuari et inanem fieri meam iniquam condemnationem); he also mentions a written appeal given by him to the papal legates at Ephesus, in which he had begged the Holy See to take cognizance of the matter (in quibus vestrae sedis cognitionem poposci). Eusebius fled to Rome, where he was kindly received by Leo I. In two letters written on the same day (April 13, 451) to Pulcheria and Anatolius, the pope bespeaks their good offices for Eusebius; in the former letter he mentions a report that the Diocese of Dorylaeum was being thrown into disorder by an intruder (quam dicitur vastare qui illi injuste asseritur subrogatus). But Liberatus (Breviarium, c. xii) says that no one was put in Eusebius's place, and the report was therefore probably of merely local origin.

Eusebius took part in the Council of Chalcedon, at which he appears as the accuser of Dioscurus. He was one of the commission which drew up the definition of faith finally adopted. The council annulled his condemnation, and made special mention of the fact in the letter to the pope in which it sought his confirmation of its acts. The rescript of the Emperor Marcian (451), issued to clear the memory of Flavian, declares the reputation of Eusebius to be uninjured by the sentence of the Robber Council (injusta sententia nihil obsit Eusebio). He was one of the bishops who signed the 28th canon of Chalcedon giving patriarchal rights over Pontus and Asia to Constantinople. When the papal legates demurred to the passing of the canon in their absence, and the signatories of the region affected were asked to declare whether they had signed willingly or not, Eusebius said that he had done so, because, when in Rome, he had read the canon to the pope, who had accepted it. Though he was doubtless mistaken as to the fact alleged (how the mistake arose cannot now be determined), his professed motive is significant. His name appears among the signatures to the acts of a council held in Rome in 503, but it seems improbable that he was alive at that date. Baronius considers that the signatures of numerous Eastern bishops appended to these acts are misplaced, and properly belong to some much earlier council; since none of the bishops are otherwise heard of later than ten years after the Council of Chalcedon, at which they had all been present.

Flavian said of Eusebius at Constantinople that "fire seemed cold to his zeal for orthodoxy", and Leo wrote of him that he was a man who "had undergone great perils and toils for the Faith". In these two sentences all that is known of him may be fitly summarized.

A. B. SHARPE