The campaigns for the conquest and conversion of the lands on the southern and eastern coast of the Baltic Sea from the late 12thcentury to the Reformation have become known as the Baltic or Northern Crusades. Attempts by Scandinavian, German, Polish, and Bohemian missionaries of pagan conversion to Latin Christianity failed before the late twelfth century, when crusaders from Sweden, Gotland and Saxony conquered most of Latvia and Estonia. The Livonian Brothers of the Sword military order provided a permanent occupation force while the crusaders wintered at home. Defeats at Saule in 1236 and at Lake Peipus in 1242 halted the order's expansion into Lithuania and Russia. From 1237, Pope Gregory IX began absorbing the Sword Brothers into the Teutonic Order. Founded in Palestine as a hospital order after the Siege of Acre in the 1190s, the Teutonic Knights were reorganised as a military order. Historian Robert Bartlett defines the conquest and organisation of power in the Baltic as part of a general movement for 'the expansion of Latin Christendom'. It was made possible by the crusading ideology placing the full machinery of the Church behind superior military technology. It enabled the recruitment of troops by preaching the offer of spiritual rewards for combatants and the administrative machinery to establish a government in the conquered territories.