Niger River
The Tabula Peutingeriana says "Flumen Girin" (River Girin) and "Hoc flumen quidam Grin vocant, alii Nilum appellant dicint enim sub terra Etyopium in Nilum ire Lacum.", which means "This river which some are naming Grin is called Nile by others and is thought to flow under the ground of Ethiopia (i.e. modern Africa) into the Nile Lake."