The Treurenberg is the hill in the upper town on which the Cathédrale des Saints-Michel-et-Gudule was built. On the rue Treurenberg stood a massive tower of the first town wall that served as a state prison from the 16th century until 1760, when it was demolished. Called the "Bastille of Brussels," the windowless prison was labeled Treurenberg, the name dating from the wars of religion. Prior to then it was called the porte Sainte-Gudule, referring to its original purpose as a city gate. "Treurenberg" signifies "Mount of Tears," or, derived from "Treuenborgh," "fortified chateau." The rue Treurenberg forms a portion of the ancient merchant road from Flanders to the Rhineland.
Historical Dictionary of Brussels. Paul F. State.