The station pipes for the Stephansplatz station lie at a distance of only 5 m from Vienna's greatest cultural monument, St. Steven's Cathedral. The foundations of the Pagan Towers go down to a depth of three meters and rest, to some extent, on settlement endangered loess soil. Before the construction work on the underground rail system was begun, a thorough investigation was made of the peculiarities of the cathedral and its reaction to the construction work, and the engineering of the underground system was planned taking these factors into account. The planners foresaw the use of bored pile walling and injection material as the best means of separating the soil directly affected by the construction work from that beneath St. Steven's. The stress and settlement of the former, it was reasoned, would, in this way, have the least possible influence upon the latter. Additional measures taken include shield tunneling with compressed air compensation to protect the immediate vincinity of the endangered zone, low-vibration erection of the bored pile walls for the adjoining open construction pits, and restriction of pit wall deformation. Measurements taken of the cathedral's reaction with respect to settlement, slope and vibration during the tunnel construction proved the measures instituted to have been altogether successful.