Glacis: The Glacis was the vast area outside the former Vienna city wall, intended as a defence plain against enemy attack and to allow cannon fire on enemy troops during sieges. An imperial decree of 1558 forbade housing construction within a distance of 50 Klafter (= 95 m) from the city moat. In 1770, trees and other plants were cultivated in this area and it was only then that it was given the name Glacis. The Viennese loved this new recreational area, especially the "Wasser-Glacis", now part of the Stadtpark. In 1857 Emperor Franz Joseph I ordered that the city should be expanded and that the Glacis was to be used as a building area. The result of this building activity was the Ringstrasse circular roadway. Until 1870 the area between Burgtor and Schottentor (the "Flegelwiese", as it was called by the Viennese), was used as a military parade ground.