from james brundage’s “E Pluribus Unum” in Regional Variations in Matrimonial Law and Custom in Europe, 1150-1600 we find out that peoples in the baltic regions were marrying close relatives (prolly close cousins) up until at least the 1200s. new converts on the “livonian frontier” were allowed to keep marrying their close relatives, just as the newly converted anglo-saxons had been, only the exemptions in the baltic case happened about six hundred years later [pgs. 37-39 - links and emphases added by me]:
“In practice, too, even substantive issues in matrimonial law could also be affected by local customs. Marriage impediments, especially those grounded on consanguinity or affinity, constituted one area of matrimonial law where custom sometimes influenced practice in a major way. Local customs in some places sought to mitigate some of the serious problems that arose from the long-standing canonical ban on marriages between persons related within seven degrees of consanguinity. Conscientious Christians who wished to marry might find it exceedingly difficult, if not utterly impossible, to do so legally under the seven-degree rule that prevailed prior to 1215. As Jean-Louis Flandrin showed, strict application of the law could literally rule out thousands of persons as potential marriage partners for a given individual. Someone living in a tiny village whose population consisted solely of the members of a dozen interrelated families literally might not know anyone at all whom he or she could legally marry. In real life, it was not unknown for couples to ignore the rules and knowingly to marry persons to whom they were related far more closely than the law allowed. When such a marriage was questioned those who could afford to do so could apply for a dispensation. Alexander III had permitted local bishops to grant these, but by the time of Innocent III (r. 1198-1216) this power was reserved to the pope, which made it more difficult, time-consuming, and costly to take advantage of this possiblity.
“Theologians and writers on pastoral concerns were keenly aware of these difficulties and on occasion complained vociferously about them. The twelfth-century Parisian theologian, Peter the Chanter (d. 1197) devoted a whole chapter of his widely-circulated ‘Verbum abbreviatum’ to a scathing criticism of the law on this matter. ‘The Lord,’ wrote Peter, ‘laid down certain immutable laws concerning marriage, according to which only twelve parties were excluded as marriage partners. To these we have added the fifth, sixth, and seventh degrees, in which we join some together and separate others who were joined together, just as we please.’
“At the beginning of his pontificate Innocent III rejected the view that customary usage could abridge the canonical rule that prohibited marriage within seven degrees of consanguinity. In 1199 he held that custom had no power to alter the existing consanguinity rules. Further experience with the difficulties that this policy created soon led him to modify his views. In 1201 Innocent received Theodric of Treiden (d. 1219), as envoy from Bishop Albert von Buxhoeveden of Riga (r. 1199-1229). Theodric presented the pope with a series of questions concerning problems that missionaries on the Livonian frontier were encountering. Two of these concerned marriage customs. One custom allowed marriage between persons related within the canonically prohibited degrees of blood relationship, while the other involved the practice of levirate marriage, whereby men were obliged to marry the widow of a brother who had died childless. In response to this query Innocent chose to follow the example of ‘Blessed Pope Gregory of holy memory’ by permitting prospective or recent converts to Christianity to observe both customs. By 1205, however, church authorities, including Innocent himself, were becoming acutely aware that the consanguinity rules frequently created intolerable problems for others than recent converts. A decade later he finally took the radical step of reducing the number of prohibited degrees from seven to four in the constitution ‘Non debet reprehensibile’ of the Fourth Lateran Council. Although this did not eliminate the problems that consanguineous marriage presented, it at least made them considerably less daunting and less common than they had previously been.”
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