Milcov River (Siret) in the context of "United Principalities"

Muntenia (Romanian pronunciation: [munˈteni.a], also known in English as Greater Wallachia) is a historical region of Romania, part of Wallachia (also, sometimes considered Wallachia proper, as Muntenia, Țara Românească, and the rarely used Valahia are synonyms in Romanian). It is situated between the Danube (south and east), the Carpathian Mountains (the Transylvanian Alps branch) and Moldavia (both north), and the Olt River to the west. The latter river is the border between Muntenia and Oltenia (or Lesser Wallachia). Part of the traditional border between Wallachia/Muntenia and Moldavia was formed by the rivers Milcov and Siret.

The Roman Catholic Diocese of Cumania was a Latin-rite bishopric west of the Siret River (in present-day Romania) from 1228 to 1241. The lands incorporated into the diocese had been dominated by the nomadic Cumans since about 1100. Catholic missions began after Andrew II of Hungary granted Burzenland to the Teutonic Knights in 1211. After Andrew expelled the Knights from the territory in 1225, Dominican friars continued the Cuman mission. Robert, Archbishop of Esztergom baptized Boricius, an influential Cuman chieftain, two years later.

Robert ordained a Hungarian Dominican friar, Theodoric, as the first bishop of Cumania in early 1228. Pope Gregory IX confirmed Theodoric's consecration on 21 March of that year, and the diocese was subordinate to the Holy See in 1229. The episcopal see was on the Milcov River, but its exact location is unknown. The diocese included Burzenland and lands east of the Carpathian Mountains. Vlachs (Romanians) who belonged to the Orthodox Church were a significant part of the diocese's population. They did not follow the Catholic bishop, and persuaded many Catholic Hungarians and Saxons to accept their Orthodox bishops.