Measured along with the Lualaba, the Congo River has a total length of 4,370 km (2,715 mi). It is the only river to cross the equator twice. The Congo Basin has a total area of about 4,000,000 km2 (1,500,000 sq mi), or 13% of the entire African landmass.
The name Congo/Kongo river originates from the Kingdom of Kongo once located on the southern bank of the river. The kingdom in turn was named for the indigenous Bantu Kongo people, known in the 17th century as "Esikongo". South of the Kingdom of Kongo proper lay the similarly named Kakongo kingdom, mentioned in 1535. Abraham Ortelius in his world map of 1564 labeled as "Manicongo" the city at the mouth of the river.
The tribal names in kongo possibly derive from a word for a public gathering or tribal assembly. The modern name of the Kongo people or Bakongo was introduced in the early 20th century.
The name Zaire is from a Portuguese adaptation of a Kikongo word, nzere ("river"), a truncation of nzadi o nzere ("river swallowing rivers"). The river was known as Zaire during the 16th and 17th centuries; Congo seems to have replaced Zaire gradually in English usage during the 18th century, and Congo is the preferred English name in 19th-century literature, although references to Zahir or Zaire as the name used by the inhabitants remained common.