The Prussian mythology was a polytheistic religion of the Old Prussians, indigenous peoples of Prussia before the Prussian Crusade waged by the Teutonic Knights. It was closely related to other [Baltic faiths, the Lithuanian and Latvian mythologies. Its myths and legends did not survive as Prussians became Germanized and extinct in early 18th century. Fragmentary information on gods and rituals can be found in various medieval chronicles, but most of them are unreliable. No sources document pagan religion before the forced Christianization in the 13th century. Most of what is known about Prussian religion is obtained from dubious 16th-century sources (Sudovian Book and Simon Grunau).