Alexander the Great in the Quran called them the Caspian 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. Several historical figures, both Muslim and Christian, searched for Alexander's Gate and several different identifications were made with actual walls. During the Middle
Alexander the Great in the Quran is no identification at all. ... Personally, I have not the least doubt that Zul-Qarnain is meant to be Alexander the Great, the historic Alexander, and not the legendary Alexander... In his commentary of the Quran, Abul Ala Maududi (1903–1979 AD) noted that historically most Muslim scholars had endorsed the identification of Dhul-Qarnayn with Alexander the Great, but recent commentators have forwarded an alternative theory that Dhul-Qarnayn is Cyrus the Great: The identification of Zul-Qarnain has been a controversial matter from the earliest times. In general the commentators have been of the opinion that he was Alexander the Great but