In the early 13th century, Estonia became one of the last regions in Europe to be Christianized, a process driven by the Northern Crusades, which targeted pagan areas in Northern Europe. Pope Celestine III first called for a crusade against the pagans of the Baltic in 1193, and by 1208, German crusaders from Riga, aided by recently converted Livs and Letts, began launching raids into southern Estonia. The Estonian tribes, divided into counties led by local elders, fiercely resisted the crusaders and at times launched their own raids on enemy territories.
The Livonian Crusade (1198–1227) was part of the broader Northern Crusades and focused on the conquest and Christianization of the Baltic region, including Estonia and Latvia. The German Sword Brethren, later merged into the Teutonic Order, played a key role, along with Denmark. In 1217, a crucial battle occurred in which the Estonian leader Lembitu of Lehola was killed, marking a significant defeat for the Estonian tribes.
By 1227, all of mainland Estonia had been conquered, and the island of Saaremaa, the last stronghold of resistance, formally accepted Christianity. Estonia was divided into feudal principalities under the control of the crusaders. The Danish king Valdemar II gained control of northern Estonia after his victory at the Battle of Lindanise (Tallinn) in 1219. Meanwhile, the Livonian Brothers of the Sword dominated southern Estonia.
German conquests. © S. Bollmann
Despite the Christian conquest, Estonian uprisings persisted. In 1223, during a brief rebellion, most Christian strongholds were captured by Estonian forces, but by 1224 the crusaders had regained control. Saaremaa resisted until 1241, and sporadic revolts continued until the final defeat of the Oeselians in 1261.
After their conquest, Estonia became part of Terra Mariana, a papal vassal state within the Holy Roman Empire. Control was divided among the Danish crown and various ecclesiastical principalities, including the Bishoprics of Dorpat (Tartu) and Ösel-Wiek. The conquest and forced Christianization marked the end of Estonia’s ancient pagan tribal structures and the beginning of its medieval history under foreign rule.