Antoninus Pius was succeeded in 161 by his adopted sons, Marcus Aurelius Antoninus Verus and Lucius Ceionius Ælius Aurelius Commodus Antoninus. Upon his accession to the throne the former transferred his name Verus to the latter, who was thenceforth called Lucius Aurelius Verus. In his Chronicle Eusebius keeps these two princes distinct, but in his History he falls into sad confusion in regard to them, and this confusion has drawn upon him the severe censure of all his critics. He knew of course, as every one did, that Antoninus Pius had two successors. In Bk. IV. chap.14, § 10, he states this directly, and gives the names of the successors as |Marcus Aurelius Verus, who was also called Antoninus,| and |Lucius.| From that point on he calls the former of these princes simply Antoninus Verus, Antoninus, or Verus, dropping entirely the name Marcus Aurelius. In Bk. IV. chap.18, § 2, he speaks of the emperor |whose times we are now recording,| that is, the successor of Antoninus Pius, and calls him Antoninus Verus. In Bk. V. Introd. § I he refers to the same emperor as Antoninus Verus, and in Bk. V. chap.4, § 3, and chap.9, he calls him simply Antoninus, while in Bk. IV. chap.13, § 8, he speaks of him as the |Emperor Verus.| The death of this Emperor Antoninus is mentioned in Bk. V. chap.9, and it is there said that he reigned nineteen years and was then succeeded by Commodus. It is evident that in all these passages he is referring to the emperor whom we know as Marcus Aurelius, but to whom he gives that name only once, when he records his accession to the empire. On the other hand, in Bk. V. chap.5, § 1, Eusebius speaks of Marcus Aurelius Cæsar and expressly distinguishes him from the Emperor Antoninus, to whom he has referred at the close of the previous chapter, and makes him the brother of that emperor. Again, in the same chapter, § 6, he calls this Marcus Aurelius Cæsar, just referred to, the |Emperor Marcus,| still evidently distinguishing him from the Emperor Antoninus. In this chapter, therefore, he thinks of Marcus Aurelius as the younger of the two sons left by Antoninus Pius; that is, he identifies him with the one whom we call Lucius Verus, and whom he himself calls Lucius in Bk. IV. chap.14 § 10. Eusebius thus commits a palpable error. How are we to explain it?
The explanation seems to me to lie in the circumstance that Eusebius attempted to reconcile the tradition that Marcus Aurelius was not a persecutor with the fact known to him as a historian, that the emperor who succeeded Antoninus Pius was. It was the common belief in the time of Eusebius, as it had been during the entire preceding century, that all the good emperors had been friendly to the Christians, and that only the bad emperors had persecuted. Of course, among the good emperors was included the philosophical Marcus Aurelius (cf. e.g. Tertullian's Apol. chap.5, to which Eusebius refers in Bk. V. chap.5). It was of Marcus Aurelius, moreover, that the story of the Thundering Legion was told (see ibid.). But Eusebius was not able to overlook the fact that numerous martyrdoms occurred during the reign of the successor of Antoninus Pius. He had the documents recording the terrible persecution at Lyons and Vienne; he had an apology of Melito, describing the hardships which the Christians endured under the same emperor (see Bk. IV. chap.26). He found himself, as an historian, face to face with two apparently contradictory lines of facts. How was the contradiction to be solved? He seems to have solved it by assuming that a confusion of names had taken place, and that the prince commonly known as Marcus Aurelius, whose noble character was traditional, and whose friendship to the Christians he could not doubt, was the younger, not the older of the two brothers, and therefore not responsible for the numerous martyrdoms which took place after the death of Antoninus Pius. And yet he is not consistent with himself even in his History; for he gives the two brothers their proper names when he first mentions them, and says nothing of an identification of Marcus Aurelius with Lucius. It is not impossible that the words Marcus Aurelius, which are used nowhere else of the older brother, are an interpolation; but for this there is no evidence, and it may be suggested as more probable that at the time when this passage was written the solution of the difficulty which he gives distinctly in Bk. V. chap.5 had not yet occurred to him. That he should be able to fancy that Marcus Aurelius was identical with Lucius is perhaps not strange when we remember how much confusion was caused in the minds of other writers besides himself by the perplexing identity of the names of the various members of the Antonine family. To the two successors of Antoninus Pius, the three names, Aurelius, Verus, and Antoninus, alike belonged. It is not surprising that Eusebius should under the circumstances think that the name Marcus may also have belonged to the younger one. This supposition would seem to him to find some confirmation in the fact that the most common official designation of the older successor of Antoninus Pius was not Marcus Aurelius, but Antoninus simply, or M. Antoninus. The name Marcus Aurelius or Marcus was rather a popular than an official designation. Even in the Chronicle there seems to be a hint that Eusebius thought of a possible distinction between Antoninus the emperor and Marcus, or Marcus Aurelius; for while he speaks of the |Emperor Antoninus| at the beginning of the passages in which he recounts the story of the Thundering Legion (year of Abr.2188), he says at the close: literæ quoque exstant Marci regis (the M. Aureli gravissimi imperatoris of Jerome looks like a later expansion of the simpler original) quibus testatur copias suas iamiam perituras Christianorum precibus servatas esse. But even when he had reached the solution pointed out, Eusebius did not find himself clear of difficulties; for his sources put the occurrence of the Thundering Legion after the date at which the younger brother was universally supposed to have died, and it was difficult on still other grounds to suppose the prince named Marcus Aurelius already dead in 169 (the date given by Eusebius himself in his Chronicle for the death of Lucius). In this emergency he came to the conclusion that there must be some mistake in regard to the date of his death, and possessing no record of the death of Marcus Aurelius as distinct from Antoninus, he simply passed it by without mention.
That Eusebius in accepting such a lame theory showed himself altogether too much under the influence of traditional views cannot be denied; but when we remember that the tradition that Marcus Aurelius was not a persecutor was supported by writers whose honesty and accuracy he could never have thought of questioning, as well as by the very nature of the case, we must, while we smile at the result, at least admire his effort to solve the contradiction which he, as an historian, felt more keenly than a less learned man, unacquainted with the facts on the other side, would have done.