region of Tartu in ca 1030, and after a victorious battle with the local tribe of Ungannians built his own fort there, and named it Yuryev. Tartu may have remained under Kievan Rus' control until 1061, when, according to chronicles, the Yuryev fort was burned down by Sosols (probably Oeselians, Sackalians, or another Estonian tribe). Soon afterwards the fort was rebuilt. In the 12th century, local Ungannians on one side and troops from the neighbouring Novgorod Republic on the other side repeatedly raided each other. In those campaigns, the invaders were reportedly able to capture Tartu in 1133 or 1134, and in the winter of 1191–1192, however these temporary captures are not known to have brought any lasting territorial changes. Medieval bishopric During the period of Northern Crusades in the beginning of the 13th century the fort of Tarbatu (or Tharbata, Tartu) was captured by the crusading Teutonic knights — also known as the Brothers of the Sword — and recaptured by Estonians on several occasions. In 1224, after the princes of Novgorod and Pskov had sent additional troops led by prince Vyachko of Kukenois to aid the Estonian defenders of the fort, it was besieged and conquered for one last time by the Teutonic crusaders. Subsequently, known as Dorpat (Latin: Tarbatum), Tartu became a commercial centre of considerable importance during the later Middle Ages and the capital of the semi-independent Bishopric of Dorpat. In 1262 the army of prince Dmitri of Pereslavl launched an assault on Dorpat, capturing and destroying the town. His troops did not manage to capture the bishop's fortress on Toome Hill. The event was recorded both in subsequent German and Old East Slavic chronicles, which also provided the first record of a settlement of German merchants and artisans which had arisen alongside the bishop's fortress. In medieval times, after the Livonian Order was subsumed into the Teutonic Knights in 1236, the town became an important trading city. In the 1280s Dorpat joined the Hanseatic League. Polish-Lithuanian and Swedish rule In 1558, tsar Ivan the Terrible invaded Tartu beginning the Livonian War. Forces under the command of Pyotr Shuiski encircled the town and began the heavy bombardment. In light of this and without any prospect of external help the town surrendered. The local bishop was imprisoned in Moscow, which effectively ended the period of local self-government. Ivan Mikhailovich Viskovatyi, a leading diplomat and archivist of diplomatic