Shibam is a city of skyscrapers built out of mud: some five hundred tower houses, up to eleven storeys, packed behind one wall on a spur above the Wadi Hadhramaut in eastern Yemen. The towers are sun-dried brick on stone footings, rendered in mud and crowned with white lime. A house like that lasts only as long as someone keeps mending it. After every rainy season the walls are patched and re-smoothed by hand; left alone, a five-hundred-year-old tower slumps and dissolves in a few years. The vertical town is younger than the town. People had held this spur for seventeen centuries when a flood in 1532 swept away the settlement on the valley floor, and the rebuilding went upward. Height was defence. The towers stand so close that the place became one fortress against Bedouin raids, and raised corridors once linked some rooftops, so a family could cross town without going down to the street.
The streets are slots. The alleys take two people at a time and wind between ten-storey walls, with daylight narrowed to a bright strip over your head and the ground cool even at midday. Every entrance you pass carries a heavy studded door and a hand-forged knocker, and no two carvings quite repeat. Above your head, wooden lattices called qamariya open into stars and rosettes, cooling the rooms and screening them from the alley. Inside, the ground floor is windowless, for grain and animals; families live in the middle storeys, and the top ones, where the air moves, are for sitting. A belt of date palms separates the wall from the wadi floor, and walking that green edge shows you how abruptly the towers begin: cultivation one moment, eleven storeys the next. At the end of the day, once the far cliffs cut the sun, the whole skyline goes orange, the pale lime crowns holding the light longest. The recipe is earth, straw and lime, and the skill for it passes down in families; the town stands up because those hands keep going.