Ancient Romans thought that the river near Timbuktu was part of the Nile River and Ibn Battuta had the same opinion. Early 17th-century European explorers thought that it flowed west and joined the Sénégal River. Many local people probably knew the real route, but Europeans only knew it in the late 19th century, when it was mentioned in the book "Travels in the Interior of Africa" by the Scottish explorer Mungo Park. This unusual route happened because the Niger River is two ancient rivers which are joined together. The upper Niger, from the source, past Timbuktu, to the bend in the river, used to empty into a lake, but the lake has now gone. However, the lower Niger started in hills near the lake and flowed south into the Gulf of Guinea. The Sahara Desert dried up in 4000-1000 BC, and the two rivers changed their routes and they joined (some people disagree, but most people think this is true).