The Treaty of Lyck was a treaty between Vytautas the Great, future Grand Duke of Lithuania, and the Teutonic Knights, represented by Marquard von Salzbach, "komtur" Arnold von Bürglen, and Thomas, son of Lithuanian duke Survila. It was signed on 19 January 1390 in Lyck, State of the Teutonic Order, (now Ełk, Poland). Vytautas, in exchange for a military alliance against his cousin Jogaila during the Lithuanian Civil War (1389–1392), agreed to cede Samogitia up to the Nevėžis River and become the Order's vassal. In essence Vytautas confirmed the Treaty of Königsberg (1384) that he had signed with the Knights during the Lithuanian Civil War (1381–1384). Once betrayed, the Knights now asked for hostages as a guarantee of Vytautas' loyalty. The Order demanded as hostages his two brothers Sigismund and Tautvilas, wife Anna, daughter Sophia, sister Rymgajla, brother-in-law Ivan Olshanski, and a number of other nobles.