Thanks to the stability of the Triassic sandstone, extensive complexes of cellars - in some places up to four storeys deep - could be excavated into the bedrock. To this day, an ingenious and amazingly simple system of ventilation shafts ensures the automatic circulation of fresh air. Originally, these rock-cut cellars were used primarily for the making and storing of beer. In fact, the first reference to their existence has to do with the storage of beer. In an ordinance of the Nuremberg town council dated November 11, 1380, it is decreed that anyone intending to brew and sell beer must have a cellar of his own, "ten feet long and sixteen feet wide." With the introduction of mechanical refrigeration, the rock-cut cellars lost their significance as beer-storage facilities. During the devastating air raids of World War II, many citizens of Nuremberg sought and found shelter in the historic beer cellars. Today, a tract of cellars directly beneath the Altstadthof Brewery is once again being used for the storage of several tasty beer specialities.