Human settlement in the Sahara Desert is limited but historically significant. Nomadic tribes, such as the Tuareg and Berbers, have traveled this desert for centuries, passing through it mainly for trade while other groups of people wouldn't dare try (understandably). There are some oases, providing vital water sources, that serve as hubs for small to medium-sized towns and cities, like Ghardaia in Algeria and Timbuktu in Mali, the latter being a UNESCO World Heritage site.