From the Roman Council of Nicholas II, A.D. 1059

Canon XI. That no one lead a wife from his own consanguinity up to the seventh generation, or as far as kinship could be known.

This last phrase is not added to extend the series of prohibited degrees beyond the seventh, but to declare the same matter in another way; for kinship generally is not known beyond the seventh degree, that is, an account of it is not usually had among men. Cf. what we shall say at the Roman Council of Alexander II.