In 1227, Saaremaa was conquered by the Livonian Brothers of the Sword during the Livonian Crusade but the resistance of the local inhabitants remained strong. The crusaders founded the Bishopric of Ösel-Wiek there. When the Order was defeated by the Lithuanian army in the Battle of Saule in 1236, the Saaremaa islanders rebelled. The conflict was ended by a treaty that was signed by the Osilians and the Master of the Order. In the following year, the Sword-Brothers were absorbed into the Teutonic Order. As the crusaders' hold on Saaremaa got stronger, Christianity also became more established on the island, and to this day Saaremaa has a unique set of medieval churches in Kaarma, Karja, Kihelkonna, Muhu, Pöide, Püha and Valjala churches. The crusader's fortress Kuressaare Castle, known in German as Schloss Arensburg, was built by the Teutonic Order for the bishops of Ösel-Wieck (Estonian: Saare-Lääne). Construction began in 1380 and it is one of the most well-preserved medieval castles in Estonia and bears testimony to the late Medieval Age.