The single most detailed surviving account of pre-Christian Scandinavian sacrificial practice comes from Adam of Bremen, a German cleric writing in the 1070s CE, describing a great festival held every nine years at the royal temple of Uppsala in Sweden. According to Adam, the rite lasted nine days, during which sacrifices were offered from every living species, animal and, he states, human, with nine males of each kind killed and their bodies hung in the sacred grove that stood beside the temple, a grove Adam describes as so hallowed by the presence of the dead and dying offerings that ordinary people avoided walking beneath its trees.
Adam links the temple itself to the worship of three principal gods, whom he names as Thor, Wodan and Fricco, generally understood as Thor, Odin and Freyr, describing their images enthroned together inside the building and noting that different petitioners favored different gods depending on their need, Thor for plague or famine, Wodan for war, Fricco for marriage and fertility, a division of divine responsibility that broadly matches patterns found elsewhere in the surviving Norse mythological corpus. Adam himself never claims to have witnessed the nine day rite firsthand, and the numeral nine recurs suspiciously often in his account, in the years between celebrations, the days of sacrifice and the victims of each kind, a repetition some modern scholars read as owing as much to the number's symbolic weight in Adam's own sources as to a precise historical count.