Re: Who exactly is Zulqurnain, as mentioned in Quran?
Alexander the ‘great’ and Cyrus of Persia are two very different people, who came around different times (Cyrus came in 600 BC, Alexander around 350 BC) with different styles of ruling. Cyrus is who we know as Prophet zulqernain who travelled vastly in the earth, building the first world empire. He built the iron wall to keep back yajooj majooj, between the black and caspian sea.
The meaning of Zulqernain is ‘two horns’ as the helemt he wore always had two horns protuding. He was a monothiest, unlike alexander. The fort gates still exist and are known as caspian gates of derbent (rooted in the persian word dar band - closed gated), but mistakenly is attributed to Alexander by some historians.
The Gates of Alexander are most commonly identified with the Caspian Gates of Derbent (*Russia](Russia - Wikipedia)) whose thirty north-looking towers used to stretch for forty kilometers between the Caspian Sea](Caspian Sea - Wikipedia) and the *Caucasus Mountains](Caucasus Mountains - Wikipedia), effectively blocking the passage across the Caucasus.
Derbent was built around the world’s only surviving Sassanid](Sasanian Empire - Wikipedia)Persian](Achaemenid Empire - Wikipedia) fortress, which served as a strategic location protecting the empire from attacks by the *Gokturks](Göktürks - Wikipedia). The historical Caspian Gates were not built until probably the reign of Khosrau I](Khosrow I - Wikipedia) in the 6th century, long after Alexander’s time, but they came to be credited to him in the passing centuries. The immense wall had a height of up to twenty meters and a thickness of about 10 feet (3 m) when it was in use.*
Although the current fortifications date to well after Alexander’s death, some scholars postulate that there might have been earlier fortifications built during the Achaemenid](Achaemenid Empire - Wikipedia) Persian Empire (the area has indeed been settled for at least 5000 years). If this is true, agents of Alexander’s empire may have visited or even strengthened them after the Achaemenids were conquered, though Alexander personally never travelled that far north.