Excerpts from sacred canons and the deeds of the holy fathers about the religious life of nuns (cultus sanctimoniae) and about the constancy of declaring the truth
From the decrees of Pope Siricius, chapter 4: That it is not allowed to obtain the betrothed of another man according to the laws of marriage
But about marital violation you asked, if one could take the betrothed girl of another in marriage. We prohibit by all means that this should happen: since the blessing which the priest places on the girl to be married is like a certain sacrilege for the faithful, if it is violated by any transgression.
In the council of Ancyra, chapter 10, about betrothed girls corrupted by others.
It pleases that girls who have been betrothed, and afterwards taken by others, should be plucked up and restored to those to whom they had been betrothed first, even if force should have been inflicted on them by the abductors.
From the decrees of Pope Innocent, chapter 20. About non-veiled virgins, if they should deviate.
Those who are not yet covered by the sacred veil, yet who have simulated that they will always remain in the virginal intent although they are not veiled: if perhaps they should marry, penance is to be done by these for some time, since their solemn promise (sponsio) was held by the Lord. For if a contract of good faith between men is not accustomed to be dissolved without reason, how much more ought that promise which they agreed with God not to be dissolved without punishment? For if the apostle Paul said that those who had departed from the intent of widowhood had condemnation, since they had made original faith invalid, how much more do virgins who have tried to break their original promise of faith?
From the decrees of Pope Leo, chapter 27. That those who, not forced but by their own will, have received the way of life of virginity, offend if they marry, even if they have not yet been consecrated.
Girls who have received the way of life and habit of virginity, not forced by the command of parents, but by their free will decision: if afterwards they should choose marriage, they are prevaricating, even if the grace of consecration should not yet reached them: whose gift they would not be cheated of if they were to remain in their way of life.
Again of the same Pope Leo to Rusticius. About girls who are now consecrated; if afterwards they should marry, they admit a double crime of both way of life and consecration.
About these who are now consecrated, if they should marry afterwards, it cannot be doubted that a great crime is admitted, where both the way of life is forsaken and the consecration is violated. For if human pacts cannot be violated with impunity, what will happen to those who break the faith of divine sacrament?
From the decrees of Pope Gelasius, chapter 20. That these who associate themselves with holy virgins, and unite in incestuous pacts, cannot communicate, unless they do public penance.
But we have learned that certain men dare to associate themselves with holy virgins and after a way of life dedicated to God, they mix incestuous crime with sacrilege. It is just that these forthwith should be expelled from Holy Communion and not received in any way unless through public and proved penance: but if they are passing away from the world, certainly the viaticum, if yet they should be penitent, is not denied to them.
From the decrees of Pope Siricius, chapter 6: about monks and virgins not preserving the way of life.
The sinning devoted woman is not to be received in church, unless she should cease to sin, and if ceasing she should do suitable penance for ten years, thus she may receive communion. And first admitted into the church for prayer, let her not approach the company (convivium) of any Christian woman, and if she is admitted, let her who received her be held at a distance. Also let an equal punishment constrain the corrupter. But she who receives a husband is not to be admitted to penance unless she begins to live chastely, while her husband is still living or after he has died.
 Klaus Zechiel-Eckes and Jasper Detlev, Die erste Dekretale: der Brief Papst Siricius' an Bischof Himerius von Tarragona vom Jahr 385 (JK 255) (Hahnsche Buchhandlung, 2013), c. 4, pp. 90-92.
 This canon is in some manuscripts transmitting Leo's letter: see Patrologia Latina 54, col. 1208 notes.
 Tenth Council of Toledo 656, c. 5, ed. Vives, Concilios visigóticos e hispano-romanos, p. 212.
 A quotation from the Epitome Iuliani, no. 115, c. 52, ed. Gustav Haenel, Iuliani epitome latina Novellarum Iustinian (Leipzig, 1873), p. 159.