By the middle of the 12th century, Vienna had become an important centre of German civilization, and the four existing churches, including only one parish church, no longer met the town's religious needs. In 1137, Bishop of Passau Reginmar and Margrave Leopold IV signed the Treaty of Mautern, which referred to Vienna as a "civitas" for the first time and transferred St. Peter's Church to the Diocese of Passau. Under the treaty, Margrave Leopold IV also received from the bishop extended stretches of land beyond the city walls, with the notable exception of the territory allocated for the new parish church, which would eventually become St. Stephen's Cathedral. Although previously believed built in an open field outside the city walls, the new parish church was in actuality likely built on an ancient cemetery dating to Ancient Roman times; excavations for a heating system in 2000 revealed graves below the surface, which were carbon-dated to the 4th century. This discovery suggests that an even older religious building on this site predated the St. Rupert's Church, which is considered the oldest church in Vienna