and water. These oases were very important. They also imported obsidian from Senegal to shape blades and other objects. The overland route through the Wadi Hammamat from the Nile to the Red Sea was known as early as predynastic times; drawings depicting Egyptian reed boats have been found along the path dating to 4000 BC. Ancient cities dating to the First Dynasty of Egypt arose along both its Nile and Red Sea junctions, testifying to the route's ancient popularity. It became a major route from Thebes to the Red Sea port of Elim, where travelers then moved on to either Asia, Arabia or the Horn of Africa. Records exist documenting knowledge of the route among Senusret I, Seti, Ramesses IV and also, later, the Roman Empire, especially for mining. The Darb al-Arbaʿīn trade route, passing through Kharga in the south and Asyut in the north, was used from as early as the Old Kingdom for the transport and trade of gold, ivory, spices, wheat, animals and plants. Later, Ancient Romans would protect the route by lining it with varied forts and small outposts, some guarding large settlements complete with cultivation. Described by Herodotus as a road "traversed ... in forty days", it became by his time an important land route facilitating trade between Nubia and Egypt, and subsequently became known as the Forty Days Road. From Kobbei, north of al-Fashir, the route passed through the desert to Bir Natrum, another oasis and salt mine, to Wadi Howar before proceeding to Egypt. The Darb el-Arbain trade route was the easternmost of the central routes. The westernmost of the three central routes was the Ghadames Road, which ran from the Niger River at Gao north to Ghat and Ghadames before terminating at Tripoli. Next was the easiest of the three routes: the Garamantean Road, named after the former rulers of the land it passed through and also called the Bilma Trail. The Garamantean Road passed south of the desert near Murzuk before turning north to pass between the Alhaggar and Tibesti Mountains before reaching the oasis at Kawar. From Kawar, caravans would pass over the great sand dunes of Bilma, where rock salt was mined in great quantities for trade, before reaching the savanna north of Lake Chad. This was the shortest of the routes, and the primary exchanges were slaves and ivory from the south for salt. One early 20th century