King Andrew II of Hungary granted Burzenland in southeastern Transylvania to the Teutonic Knights in 1211, tasking them with defending his kingdom's borders and converting the neighboring Cumans. The king also authorized the Knights to erect wooden fortresses and expand their authority over the Carpathians. The Knights were allowed to invite colonists to their lands, and settlers were exempted from church tithes. According to a non-authentic papal bull written almost a decade later, their territory extended as far as the lower Danube and the "borders of the Brodniks" (the Siret region) in 1222. Papal letters also stated that an unspecified number of Cumans and their wives and children were willing to convert after the Knights defeated them. The Cumans' power diminished sharply after the Mongol victory over a coalition of Rus' princes and Cuman chieftains in the 23 May 1223 Battle of the Kalka River.