In 1226, one of the regional Piast dukes, Konrad I of Masovia, invited the Teutonic Knights to help him fight the Baltic Prussian pagans, allowing the Teutonic Knights use of Chełmno Land as a base for their campaign. This resulted in centuries of warfare between Poland and the Teutonic Knights, and later between Poland and the German Prussian state. The first Mongol invasion of Poland began in 1240; it culminated in the defeat of Polish and allied Christian forces and the death of the Silesian Piast Duke Henry II the Pious at the Battle of Legnica in 1241.