Sudan is a country in northeastern Africa. It is the largest in the African continent and the Arab World, and tenth largest in the world by area. It is bordered by Egypt to the north, the Red Sea to the northeast, Eritrea and Ethiopia to the east, Kenya and Uganda to the southeast, Democratic Republic of the Congo and the Central African Republic to the southwest, Chad to the west and Libya to the northwest. The country's name derives from "Sudd", which refers to a vast expanse of floating water plants or swamps. The earliest mention of the word "Sudd" in reference to modern Sudan appear in the writings of Seneca, who recorded an expedition sent by the Roman Emperor Nero to central Sudan in the first century A.D. Later in history, Arab writers, unaware of the origin of the word "Sudan," interpreted the term as being derived from the Arabic word "Soud," meaning "Blacks.