the eastern regions of Natangia, Barta and Warmia; Thorn (Toruń), Culm (Chełmno), and Rehden (Radzyń Chełmiński) in the western parts. In December 1242, the Knights were able to capture Sartowice, Swantopolk's castle on the banks of the Vistula. The ensuing five-week siege of Sartowice failed to recapture the fortress and Swantopolk lost 900 men. In the spring of 1243, Swantopolk also lost the castle at Nakel (Nakło nad Notecią), which dominated trade on the Noteć River. In the face of these losses, the duke was forced to make a short-lived truce. 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 15 June 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). The Teutonic Knights managed to gather a coalition against Swantopolk: Dukes of Masovia were given territories in Prussia, Dukes of Greater Poland received Nakel, and Dukes of Pomerellia, brothers of Swantopolk, hoped to regain their inheritance. Swantopolk built a castle at Zantyr, where Nogat separated from the Vistula, and launched a blockade of Elbing and Balga. While the castle withstood Teutonic attacks, the blockade was smashed by cogs. In late 1245 Swantopolks's army suffered a great defeat at S(ch)wetz Świecie, and another one in early 1246, where 1,500 Pomeranians were killed. Swantopolk II asked for a truce and Pope Innocent IV appointed his chaplain, Jacob of Liège, the future Pope Urban IV, to handle the peace negotiations. However, the war was renewed in 1247 when large Teutonic reinforcements arrived in Prussia. On Christmas Eve of 1247 the Knights besieged and overwhelmed a major Pomeranian fortress, which they later renamed Christburg (Dzierzgoń), and newly arrived Henry III, Margrave of Meissen subdued the Pogesanians. Swantopolk retaliated and destroyed Christburg, but the Knights rebuilt it in a new location. Both Prussian and Swantopolk's armies failed to capture the new castle. Otto III of Brandenburg raided Warmia and Natangia, forcing the locals to surrender. The peace talks that began in 1247 achieved little, but a new truce was arranged in September 1248 and peace was made on 24 November 1248. Swantopolk had to return lands seized from his brothers, allow Teutonic Knights to pass through his domains, stop charging tolls on ships using the Vistula,