1 March: Establishment of the First Tetrarchy: Augustus Diocletian in Nicomedia; Augustus Maximian in Milan; Caesar Galerius in Thessalonike; Caesar Constantius in Trier.
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Constantius separates from Helena and in turn marries Theodora, daughter of Augustus Maximian and Helena.
Constantine remains at the court of Diocletian at Nicomedia, while the whereabouts of Helena are uncertain.