"When tourists visit sub-Saharan Africa, they often wonder 'Why there are no historical buildings or monuments?' The reason is simple. Europeans destroyed most of them. We only have a few drawings and descriptions by travelers who visited the places before their destruction. In some places, ruins are still visible. Many cities were abandoned when Europeans brought exotic diseases (smallpox and influenza) which started spreading and killing people. Most of those cities lie hidden. In fact the biggest part of Africa history is still under the ground."
Via Seth Dixon