Panama is a republic in Central America, bounded by Colombia to the east, Costa Rica to the west, the Caribbean Sea to the north, and the Pacific Ocean to the south. The narrowest point of North America, it was long considered suitable for the construction of a transisthmian access as far back as the Spanish conquistadors in the 1520s. The earliest human evidence dates to the late Pleistocene period. The isthmus was settled by Cueva, Chocoan, and Chibchan peoples prior to the arrival of Spanish conquistador and explorer Rodrigo de Bastidas in 1501. Exploration by Vasco Núñez de Balboa in 1513, confirmed the region as having the most direct route between the Caribbean Sea and Pacific Ocean, and became a vital crossroad of Spanish trade in the Americas. Between 1538–1821, Panama was part of the Spanish Empire, and until 1903, a department of Colombia. Construction of the Panama Canal was started by the French in 1881, and completed by the United States in 1914. In 1979, Panama assumed sovereignty over the Panama Canal Zone. The capital and largest city is Panama City. The population of Panama in the 2013 census was 3,661,868.