(sworn brotherhood), a custom according to which two or more persons unrelated by blood established a relationship that had the same status as blood kinship. Like other forms of artificial kinship, such as astalychestvo (the giving away of newborn children by parents of the nobility to be brought up in the families of vassals or servants), pobratimstvo was widespread during the disintegration of the primitive communal system, when it helped compensate for weakening family ties. The custom survived vestigially in class society as well.
Sworn brothers were obliged to help each other when in need or in danger; among some peoples, such as the Montenegrins, they were even obliged to take part in blood feuds. The establishment of pobratimstvo was accompanied by an oath and by ceremonial rites, usually the symbolic mingling and drinking of blood.