Trent

How did a company of women committed to apostolic service of the poor end up as cloistered nuns? Between the death of St. Ursula and the approval of her rule, the Council of Trent met and issued the following directive for religious women:

The holy council, renewing the constitution of Boniface VIII*, which begins, “Periculoso,” commands all bishops by the judgment of God to which it appeals and under threat of eternal malediction, they make it their special care that in all monasteries subject to them by their own authority and in others by the authority of the Apostolic See, the enclosure of nuns be restored wherever it has been violated and that it be preserved where it has not bee violated; restraining with ecclesiastical censures and other penalties, every appeal being ser aside, the disobedient and gainsayers, even summoning for this purpose, if need be, the aid of the secular arm. The holy council exhorts all Christian princes to furnish this aid, and binds thereto under penalty of excommunication to be incurred ipso facto all civil magistrates. No nun shall after her profession be permitted to go out of the monastery, even for a brief period under any pretext whatever, except for a lawful reason to be approved by the bishop; any indults and privileges whatsoever notwithstanding. Neither shall anyone, of whatever birth or condition, sex or age, be permitted, under penalty of excommunication to be incurred ipso facto, to enter the enclosure of a monastery without the written permission of the bishop or superior.
Twenty-fifth Session, Chapter V

*In 1298 Boniface VIII promulgated his celebrated Constitution "Periculoso” in which he imposed the cloister on all nuns. According to this law all egress was forbidden to them. In 1566 Pope St. Pius V urged the following of Boniface's law and imposed the cloister even on the third orders.