If the third period was relatively quiet the fourth was absolutely stirring. There had undoubtedly been more or less fighting along the Danube frontier during the preceding years, but early in this period there was a most important campaign against the Sarmatians, in which they were defeated and their king taken prisoner. 3029 In honor of this victory coins were struck (Eckhel, Doct. Num. Vet. 8 (1827) 87). But this was only skirmishing; afterwards came the tug of war. Nine years of peace proved the utmost limit of mutual patience, and Constantine and Licinius came to words, and from words to blows. For a long time Constantine had been vexed at the persecution of the Christians by Licinius (cf. Euseb. H. E. 10. 8, 9), persecutions waged perhaps with the express purpose of aggravating him. 3030 Licinius, on the other hand, naturally chagrined over the previous loss of territory, knowing of Constantines indignation over his persecutions, and perhaps suspecting him of further designs, was naturally suspicious when Constantine passed within his boundaries in pursuing the Sarmatians (Anon. Vales. p. 474). Mutual recriminations and aggravations followed. Licinius would not let the Sarmatian coins pass current and had them melted down (Anon. Contin. Dio. Cass., in Müller, Fragm. Hist. Gr. 4  199). Altogether they soon came to blows. The steps were short, sharp, decisive. Constantine defeated Licinius by land (July 3, 323), and through Crispus, by sea (Soz. 1. 7; Anon. Vales. p. 474–5; Zos. 2. 22–3). After the defeat at Adrianople, Licinius retreated to Byzantium (Zos. 2. 23–5; Vict. p. 419 Epit. p. 50), and then to Chalcedon (Anon. Vales. p. 475, Zos. 2. 25–6). Two months after the first victory (Sept. 18) a final and decisive battle was fought at Chrysopolis 3031 (Anon. Vales. p. 475; Socr. 1. 4). Licinius surrendered on condition that his life should be spared (Zos. 2. 28), or rather Constantia secured from her brother the promise that his life should be spared (Anon. Vales. p. 475; Vict. Epit. p. 50; Pseudo-Leo, p. 85, &c.). He retired to Nicomedia, residing at Thessalonica (Soz. 1. 7; Pseudo-Leo, &c.), but was put to death the following year. 3032 Constantine was now sole emperor. His first act (Soz. 1. 8) was to issue a proclamation in favor of the Christians (Soz. l.c.; V. C. 2. 24- , and 48- ). This was followed by many other acts in their favor,—building of churches, &c. (cf. Euseb. V. C., and notes). From this time on he was much identified with Christian affairs, and the main events are given in extenso by Eusebius (see various notes). In 325 (June 19-Aug. 25) the Council of Nicæa was held (cf. Euseb. V. C. 3. 6, and notes), and Constantine took an active part in its proceedings. The same year his Vicennalia were celebrated at Nicomedia (Euseb. V. C. 1. 1; Hieron.; Cassiod.) and the following year at Rome also (Hieron., Cassiod., Prosper, Idat.), Constantine being present at both celebrations, 3033 being thus at Rome in July, and passing during the year as far as Arles, apparently spending some time at Milan (cf. the various laws in Clinton, v. 2, p. 92).
Zos. 2. 21. An exhaustive discussion of this is that by Bessell, Gothen, in Ersch u. Gruber, Encykl. I. 75 (Leipz. 1862), 132–33. The same article (p. 133–35) discusses various relations of Goths and Sarmatians with Constantine.418:3030
According to Sozomen, Licinius withdrew his favor from Christians and persecuted them, because “He was deeply incensed against the Christians on account of his disagreement with Constantine, and thought to wound him by their sufferings; and, besides, he suspected that they earnestly desired that Constantine should enjoy the sovereign rule” (1. 7). In this view of the case, it is easy to see how and why affairs marched as they did. Eusebius (H. E. 10. 9) makes this, like the war against Maxentius, a real crusade in behalf of the persecuted Christians.419:3031 419:3032 419:3033