While few Algerians live in such hostile terrain, a chain of extraordinary hilltop settlements exist on the northern fringes of the Sahara: the five historic ksours, or fortified cities, of the M’Zab Valley. Collectively known as the Pentapolis, these magnificent, centuries-old citadels were built along the Wadi Mzab, a partially dry riverbed whose waters rise just once every three to five years. The towns include El-Atteuf, the oldest, founded in 1012; Melika; Bounoura; the Holy City of Beni-Isguen; and Ghardaïa (pictured), the principal settlement and commercial heart of the valley. In 1982, the M’Zab was classified as a Unesco World Heritage site due to its highly distinctive culture and architecture. “What makes the place so special is the unique combination of [the indigenous people of North Africa] with Ibadi Islamic beliefs who built fortress homes in the middle of the desert,” said local guide Khaled Meghnine. “There’s nowhere like it in Algeria, nor the rest of the world.” (Credit: Simon Urwin)