The Great Wall of Gorgan in Iran is 195km long, making it the second-longest wall in history behind the Great Wall of China.
The Great Wall of Gorgan is a series of connected mud- and fired-brick walls, interspersed with a series of thirty forts. It begins at the Caspian Sea and ends 195 kilometres away, in the Pishkamar Mountains of modern Iran.
Now, that’s a whole lot shorter than the Great Wall of China, but it is still longer than any other defensive wall ever built. Hadrian’s Wall, between Roman Britain and free Caledonia, is shorter than this Great Wall by 78km.
The Great Wall of Gorgan was probably built by the Sasanian Empire in the 5th or 6th Century to keep out the White Huns. Medieval tradition connects it with Alexander the Great and his legendary Caspian Gates, but he probably died centuries before construction of this edifice even began.
You can still see parts of the wall today, if you don’t mind venturing into Iran.