al-Siq (translated: the shaft) is the main entrance to the ancient city of Petra in southern Jordan. The dim, narrow gorge (in some points no more than 3 meters wide) winds its way approximately one mile and ends at Petra's most elaborate ruin, Al Khazneh (The Treasury). The Siq is a natural geological fault produced by tectonic forces and worn smooth by water erosion. The walls that enclose the Siq stand between 91-182 meters (300-600 feet) in height.