sentences:  In the summer of 1243, Prussians with Sudovian help raided the Culmerland (Chełmno Land) and, on their way back, defeated the pursuing Teutonic Knights on June 15 on the banks of the Osa River.Some 400 Teutonic soldiers perished, including their marshal.Swantopolk, encouraged by the defeat, gathered an army of 2,000 men and unsuccessfully besieged Culm (Chełmno).