Also known as Al-Kharija ,( the Outer Oasis), Kharga lies on the route of the Darb al-Arbein, the 40 Days Road which runs from Sudan to Middle Egypt. It is the largest of the Western Desert oases and the furthest from Cairo. Luxor is, in fact, the closest town to it. The Ancient Egyptians knew it as the Oasis of Thebes or the Southern Oasis. Surrounded by mountains and long rows of sand dunes there are a number of passes that lead into the oasis which have been used by travellers through the ages. The arc-shaped, barchan dunes would long ago have smothered the oasis if it were not for the mountains. Even today they threaten the cultivated land and cause families in some areas to build extra stories onto their homes to stay above the level of the encroaching sand. Kharga was once under the sea and there are still many fossils to be found and the herbivorous dinosaur Ornithischian was also found here. Another feature unique to Kharga, are the large group of yardangs. A yardang is a wind-abraded ridge typically about three times longer than they are wide, and when viewed from above, resemble the hull of a boat.