Transylvania as originally defined in Treaty of Trianon, 27 years earlier, thus confirming the return of Northern Transylvania to Romania. From 1947 to 1989, Transylvania, along with the rest of Romania, was under a communist regime. The ethnic clashes of Târgu Mureș occurred between ethnic Romanians and Hungarians in March 1990 after the fall of the communist regime and became most notable inter-ethnic incident in the post-communist era. The Transylvanian Plateau, high, is drained by the Mureș, Someș, Criș, and Olt rivers, as well as other tributaries of the Danube. This core of historical Transylvania roughly corresponds with nine counties of
History of Transylvania organization of the Transylvanian Catholic episcopacy (with Gyulafehérvár as its seat), which was finished in 1009 when the bishop of Ostia (as papal legate) visited Stephen and they approved diocesan divisions and boundaries. In 1018 Stephen defeated Ahtum, ruler of the country around the lower Mureș River. According to the "Chronicon Pictum", Stephen I also defeated the legendary Kean (a ruler in southern Transylvania of Bulgarians and Slavs). During the 12th century, the Székelys were brought to eastern and southeastern Transylvania as border guards. In the 12th and 13th centuries, the areas in the south and northeast were settled by