Gates. Twenty and two Kings did I shut up therein. These pseudepigraphic letters from Alexander to his mother Olympias and his tutor Aristotle, describing his marvellous adventures at the end of the World, date back to the original Greek recension α written in the 4th century in Alexandria. The letters are "the literary expression of a living popular tradition" that had been evolving for at least three centuries before the Quran was written. Medieval accounts of Alexander's Wall Several historical figures, both Muslim and Christian, searched for Alexander's Gate and several different identifications were made with actual walls. During the Middle Ages, the Gates of Alexander story was included in travel literature such as the Travels of Marco Polo (1254–1324 AD) and the Travels of Sir John Mandeville. The Alexander romance identified the Gates of Alexander, variously, with the Pass of Dariel, the Pass of Derbent, the Great Wall of Gorgan and even the Great Wall of China. In the legend's original form, Alexander's Gates are located at the Pass of Dariel. In later versions of the Christian legends, dated to around the time of Emperor Heraclius (575–641 AD), the Gates are instead located in Derbent, a city situated on a narrow strip of land between the Caspian Sea and the Caucasus mountains, where an ancient Sassanid fortification was mistakenly identified with the wall built by Alexander. In the Travels of Marco Polo, the wall in Derbent is identified with the Gates of Alexander. The Gates of Alexander are most commonly identified with the Caspian Gates of Derbent whose thirty north-looking towers used to stretch for forty kilometres between the Caspian Sea and the Caucasus Mountains, effectively blocking the passage across the Caucasus. Later historians would regard these legends as false: The gate itself had wandered from the Caspian Gates to the pass of Dariel, from the pass of Dariel to the pass of Derbend [Derbent], as well as to the far north; nay, it had travelled even as far as remote eastern or north-eastern Asia, gathering in strength and increasing in size as it went, and actually carrying the mountains of Caspia with it. Then, as the full light of modern day come on, the Alexander Romance ceased to be regarded as history, and with it Alexander's Gate passed into the realm of fairyland. In the Muslim world, several expeditions were undertaken to try to find and study Alexanders's