Up north, Nigeria's second largest city (pop. nearly 3 million) is a thriving metropolis with an old quarter that though dwindling still preserves some of ancient mud houses and narrow lanes which hark back to the Kingdom of Kano (1000-1349). And the most impressive remnants of that era is this 14km of mud defensive walls, started at the end of the 11th century, completed by the mid-14th, and further extended in the 16th. Originally 30 to 50 feet high, 40 feet thick at the base. In addition to 15 gates they also have associated sites like the emir's palace and the Kurmi Market (where you can still go to buy traditional crafts, especially leather, clothing, and other textiles).
Today not surrounding but inside the city which has expanded beyond them, more than half of the walls is largely pulled down or in ruins, but some intact sections do remain, like the one pictured here. Incredibly, though, it appears that though they're a UNESCO World Heritage Site, they're not being sufficiently protected by the Nigerian government, so degradation and even in some cases new construction is threatening their future. So come see this remarkable sight while you can!