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www.newadvent.org:
Henceforth, Constantine was sole master of the Roman Empire. Shortly after the defeat of Licinius, Constantine determined to make Constantinople the future capital of the empire, and with his usual energy he took every measure to enlarge, strengthen, and beautify it. For the next ten years of his reign he devoted himself to promoting the moral, political, and economical welfare of his possessions and made dispositions for the future government of the empire. While he placed his nephews, Dalmatius and Hannibalianus in charge of lesser provinces, he designated his sons Constantius, Constantine, and Constans as the future rulers of the empire. Not long before his end, the hostile movement of the Persian king, Shâpûr, again summoned him into the field. **When he was about to march against the enemy he was seized with an illness of which he died in May, 337, after receiving baptism. **