Stretching from the Sea of Marmara to the Golden Horn, these great city walls were built just in time by Emperor Theodosius II in the 5th-century to repel an attack by Attila the Hun. They formed the western boundary of the Old City for a thousand years until the Ottomans breached them with some finality in 1453. Today the ruins still give a sense of their once near-mythical indomitability. Better still, you can walk the length of the wall, sometimes on top of it, passing through some of the most diverse areas of the city, from the ex-Greek suburb of Fener through a predominately Kurdish neighbourhood, right down to the Yedikule Fortress by the Sea of Marmara. Notable points along the way include the Gate of Romanos, where Constantine XI, the last emperor, fell before Mehmet’s army, and Edirnekapi, where Mehmet made his victorious entry after blasting the wall with a specially-made super-canon, Orban, which he had cast in Hungary. The gun was so large that it took three hours to reload but the damage is still in evidence today.