Among the Romans, alliances between persons under the same _patria potestas_—_i.e._, _cognati_ related within the sixth degree—were _nefariæ et incestuæ nuptiæ_; but these prohibitions were gradually relaxed. From the time of the Second Punic War, according to Livy, even first cousins were allowed to intermarry; and in 49 A.D. the Emperor Claudius, wishing to marry his niece Agrippina, obtained from the Senate a decree that marriage with a brother’s daughter should be legal, though marriage with a sister’s daughter remained illegal.[1842] In the fourth century, however, Constantius again forbade such unions, on pain of death.[1843] Afterwards, under the influence of the ascetic ideas prevalent in the Church, the prohibited degrees were gradually extended. Theodosius the Great forbade under the severest penalties the union of first cousins, paternal and maternal; and at the end of the sixth century the prohibition was extended even to the seventh degree. This prohibition continued in force until in the Western Church it was once more reduced to the fourth degree by the Lateran Council under Innocent III. in the year 1215; that is, marriage was permitted beyond the degree of third cousins.[1844] Such is the nominal law at the present time wherever the canon law prevails.[1845] Besides the prohibitions relating to actual kinship, there are, among several peoples, others applying to marriage between relatives by alliance. Among the Andamanese, a man or woman may not marry into the family of a brother-in-law or sister-in-law.[1846] The Eastern Greenlanders and the Eskimo of the north-east coast of America forbid or disapprove of marriage with two sisters;[1847] and, according to Dr. Daniell, the same rule prevails among the natives of Accra at the Gold Coast, who even prohibit a man from marrying two cousins of the same parentage.[1848] Again, several tribes in Western Victoria do not permit marriage with a deceased wife’s daughter by a former husband.[1849] But prohibitions of this sort do not seem to be very common among savage and barbarous races. In many of the Indian tribes of North America, all the daughters of a family are, as a rule, married to the same man. A brother very frequently marries his deceased brother’s widow; and, in Africa, a son often weds all his father’s widows except his own mother.