document — Palmieri, On Christian Marriage
From the Council of Mainz, under Rabanus, A.D. 847
Canon XX. For parricides ... it will not be lawful further to take up the belt of military service and to be coupled to nuptials or marriages, because the sacred canons do not consent to this for them.
An impeding impediment of crime, constituted not now but previously.
Canon XXIX. If anyone has led a widowed wife and afterward has fornicated with his stepdaughter, or has married two sisters, or if any woman has married two brothers or [has been] with a father and son; likewise, if anyone has violated by carnal conjunction the widow of his brother, who almost before had existed as a sister; if anyone has accepted a niece in marriage; if anyone has led his stepmother or his daughter-in-law; if anyone has impudently associated himself to his female cousin, or has been polluted by concubitus with the widow or daughter of his maternal uncle or the daughter of his paternal uncle, or his own stepdaughter (now from the beginning that has been expressed), or has been stained by the touch of a conjunction of this sort: we wish them to be disjoined and never to be coupled to another marriage, but to be placed under great strictness.
Cf. Canon LVI of the Council of Mainz, A.D. 813. Nevertheless the Council of Worms, A.D. 868, Canons XXXIII, XXXVI, XXXVII, after penance had been performed, removed the prohibition of legitimate marriage for incestuous persons of this sort. Cf. also the following Council of Pavia.
Canon XXX. We also forbid that anyone hereafter be coupled in marriage in the fourth generation; but where, after the prohibition has been made, it shall have been found, let it be separated. Certainly the same rule which is to be observed in the husband's kinship must likewise be observed in the wife's kinship from the law of nuptials. Therefore, because it is established that those two are in one flesh, a common kinship on both sides must be believed to belong to them.
Cf. the sentence of Rabanus on this matter, brought forward by us after the epistles of Gregory the Great.