Emperor Maximian, having married his daughter, Fausta, to Constantine, renounced the purple and went into retirement, but the enforced idleness and his desire for power and action, induced him to again resume the imperial power. In the field near Lodi, where the oath of allegiance of the army has been received, Maximian begins his triumphant return, and we see him again amid the people crowding the streets, impatient to see him again. He enters the imperial court where Constance, a sister of Constantine, and Licinius, the young Caesar of Illyrium, and Fausta are waiting the arrival of their august relation. The love affair between Constance and Licinius is discovered by Fausta, who has instructions to prevent this alliance from being consummated, as Maximian himself has set his heart on winning Constance.