White Serbs, an early Slavic tribe from White Serbia eventually settled in an area between the Sava river and the Dinaric Alps. By the beginning of the 9th century, Serbia achieved a level of statehood. Christianization of Serbia was a gradual process, finalized by the middle of the 9th century. In the mid-10th-century, the Serbian state stretched between the Adriatic Sea, the Neretva, the Sava, the Morava, and Skadar. During the 11th and 12th century, Serbian state frequently fought with the neighbouring Byzantine Empire. Between 1166 and 1371 Serbia was ruled by the Nemanjić dynasty (whose legacy is especially cherished), under whom the state was elevated to a kingdom in 1217, and an empire in 1346, under Stefan Dušan. Serbian Orthodox Church was organized as an autocephalous archbishopric in 1219, through the effort of Sava, the country's patron saint, and in 1346 it was raised to the Patriarchate. Monuments of the Nemanjić period survive in many monasteries (several being World Heritage sites) and fortifications.