The immediate cause of his forsaking the world was as follows. His father Sergius Onesti, a man of a proud and passionate disposition, and wholly given to worldly things, had a violent quarrel with a relative about the possession of a certain meadow; so resolutely determined was he to press his quarrel to the end, that perceiving Romuald to be but half-hearted in it, and more fearful of blood-guiltiness, than desirous for the victory of his house, he threatened to disinherit him unless he displayed more zeal in the cause. The relation being equally resolved, the dependents on both sides were armed, and a fight ensued; at which Romuald, in spite of his scruples, was obliged to be present. The relation fell by the hand of Sergius himself; and Romuald, horror-stricken at the crime, of which his enforced presence at its perpetration seemed to make him a partaker, fled to the Monastery of S. Apollinaris in Classe, intending there to expiate his guilt by a penance of forty days.
During the performance of this penance he was by some means attracted to the society of a lay-brother in the monastery, and in the intervals of his penitential exercises had many conversations with him. This lay-brother, a truly spiritual man, perceiving in Romuald signs of a vocation to the religious life, strongly urged him to forsake the world altogether and at once. For this, however, Romuald was not yet prepared, and, without absolutely rejecting the advice of his friend, yet resisted, and put him off from day to day. At last one day in the course of a talk upon the visions of the Saints, the lay-brother asked him what he would give for a sight of the blessed martyr Apollinaris, the patron of the monastery. Romuald replied that for such a favour he would consent to forsake the world. That same night watching in prayer in the monastery church, they beheld a supernatural brightness issue from the high altar and fill the whole church. This was the precursor of the appearance of the blessed martyr, who came forth from the midst of the high altar habited in priestly vestments, and with a golden censer in his hand; with this he went round the church and censed each altar in its turn; and having done this, retired as he had come, leaving the church once more in darkness. His friend immediately claimed the fulfilment of the promise. But even a second vision of the martyr failed to overcome his reluctance, and he still held off. But one day praying in the church before this very altar, a sudden access of the love of God came over his soul. In a moment all his fears, all his lingering affection for worldly things vanished; he hastened to the brethren, and humbly besought them to receive him as a novice. This, however, in dread of his father's resentment, they refused to do; Romuald, once resolved, would yield to no difficulties, and betook himself at once to the Archbishop of Ravenna, laid his case before him, and asked for his help. The Archbishop, moved by the earnestness and fervour of the youth, took up his cause, and on his assurances of protection against the violence of Sergius, the brethren consented to receive him; and Romuald entered upon the course from which throughout a long life he was never to swerve, in which his ardour was to know no cooling, and which was to end in peopling many of the solitary places of Italy with refugees from the wickedness and perils of, perhaps, the most troublous time which Europe has ever known.