The canon law of the Catholic Church severely restricted the contraction of marriage (Marriage, contraction of) between relatives (Kinship). Marriage was originally prohibited up to the seventh degree of kinship, but this limitation was reduced to the fourth degree at the Fourth Lateran Council in 1215 (see Incest 2.), albeit with a stricter calculation of degrees. In principle this regulation of Catholic canon law is still in force.
The canon law prohibiting marriage within certain degr…