Cross River State is a state in the South-South geopolitical zone of Nigeria. Named for the Cross River, the state was formed from the eastern part of the Eastern Region on 27 May 1967. Its capital is Calabar, it borders to the north through Benue state, to the west through Ebonyi state and Abia state, and to the southwest through Akwa Ibom state,while its eastern border forms part of the national border with Cameroon. Originally known as the South-Eastern State before being renamed in 1976, Cross River state formerly included the area that is now Akwa Ibom state, which became a distinct state in 1987. Of the 36 states in Nigeria, Cross River state is the nineteenth largest in area and 27th most populous, with an estimated population of over 3.8 million as of 2016. Geographically, the state is mainly divided between the Guinean forest–savanna mosaic in the far north and the Cross–Sanaga–Bioko coastal forests in the majority of the interior of the state. The smaller ecoregions are the Central African mangroves in the coastal far south and a part of the montane Cameroonian Highlands forests in the extreme northeast. The most major geographical feature is the state's namesake, the Cross River, which bisects the state's interior before forming much of the state's western border, and flowing into the Cross River Estuary. Other important rivers are the Calabar and Great Kwa rivers, which flow from the inland Oban Hills, before flanking the city of Calabar and flowing into the Cross River Estuary as well. In the forested interior of the state are several biodiverse protected areas including the Cross River National Park, Afi Mountain Wildlife Sanctuary, and Mbe Mountains Community Forest. These wildlife reserves contain populations of Preuss's red colobus, African forest buffalo, bat hawk, tree pangolin, grey-necked rockfowl, and West African slender-snouted crocodile, along with some of Nigeria's last remaining Nigeria-Cameroon chimpanzee, drill, African forest elephant, and Cross River gorilla populations. Modern-day Cross River state has been inhabited by several ethnic groups for hundreds of years, primarily the Efik of the riverside south and Calabar; the Ekoi (Ejagham) of the inland south; the Akunakuna, Boki, Bahumono, and Yakö (Yakurr) of the central region; and the Bekwarra, Ogoja, Bette, Igede, Ukelle (Kukele) of the northern region. In the pre-colonial period, what is now Cross River state was divided between its ethnic groups with some joining the Aro Confederacy, while the