Simon Grunau in the context of "Prussian mythology"

Prussian mythology is the account of what is known of the polytheistic religion of the Old Prussians, indigenous peoples of Prussia before the Prussian Crusade waged by the Teutonic Knights. This archaic Indo-European religion was closely related to other Baltic faiths, namely those of the Lithuanians and Latvians. Its myths and legends did not survive because the Old Prussian people became Germanized and their culture became extinct in the early 18th century. Fragmentary information on gods and rituals can be found in various medieval chronicles, but most of this is unreliable. No sources document pagan religion before the forced Christianization in the 13th century. Most of what is known about Prussian religion has been recovered from dubious 16th-century sources (Sudovian Book and Simon Grunau).