From the First Lateran Council, Ecumenical, A.D. 1123

Canon V. We prohibit conjunctions of blood-relatives from being made, since both divine laws and the laws of the age prohibit them. For the divine laws, doing this, not only cast out both them and those who proceed from them, but call them accursed; but the laws of the age call such persons infamous and repel them from inheritance. Therefore we, following our Fathers, mark them with infamy and judge that they are infamous.

Canon XXI. We utterly forbid priests, deacons, subdeacons, and monks to have concubines or to contract marriages; we also judge that marriages contracted by persons of this sort are to be disjoined and that the persons ought to be reduced to penance, according to the definition of the sacred canons.

You see that the Fathers of this ecumenical Council appeal to preceding canons, not establish a new matter. Cf. Canon VII of the Council of Girona and the Fourth Council of Troyes, and the places cited there. Certainly the decrees of the Pontiffs of the eleventh century had regard to this, especially those of Gregory VII against concubinary clerics, who were so called because they were unequal to contracting legitimate nuptials. Therefore although in this First Lateran Council, and also more clearly in the Second, a universal law was enacted invalidating these nuptials, nevertheless that law was not simply new. Hence it is clear how ineptly it was said that Boniface VIII was the first to assert that a vow of chastity emitted in ordination renders nuptials null (from the Syllabus of Pius IX, prop. 22). For, 1. long before Boniface the nuptials of bishops, priests, deacons, and subdeacons were null by the constitution of the Church; 2. what seems more probable to Sanchez (Book VII, disp. 27, n. 10), this obligation of continence was and is from a vow, either expressed or tacit, in the very reception of the order, which the Church annexed to the order; 3. but although someone freely receiving an order should not wish actually to emit a vow, nevertheless he would be obliged to continence, and his subsequent nuptials would be null. These things also held good before Boniface. Of what matter, therefore, is Boniface the author? He first authentically declared that "the solemnity of a vow was introduced by the sole constitution of the Church (c. un. de Voto in 6)." With this principle supposed, the same Pontiff, to the question proposed to him, namely what vow ought to be called solemn and efficacious for diriming marriage, answers (ibid.): "that vow alone ought to be called solemn, as regards diriming a marriage after it has been contracted, which shall have been solemnized by reception of sacred order or by an express or tacit profession made to one of the religions approved by the Apostolic See." In this response the law of this impediment diriming the nuptials of those who are bound by such vows is not affirmed for the first time, nor first established; but it is only affirmed that these vows alone are solemn with regard to the effect of diriming a subsequent marriage. But all these things are ineptly confused in that proposition.