The investigation of undiscovered territories. The urge to travel is as old as humanity, with the first humans probably spreading out from Africa, and possibly Asia, across the globe. The Native Americans of both North and South America probably walked there over land-bridges from what is now Russia, some 30,000 years ago. For the early European explorers, travel was easier by sea than by land: Phoenician traders frequently sailed to Galicia (in Spain) and Brittany, and perhaps even to Cornwall.
In the early Middle Ages the Vikings sailed as far west as Greenland and to North America and curiosity about the “marvels of the east” led the Italian Marco Polo overland to China (1271–95). Meanwhile, the Chinese Ming emperors supported the seven voyages of discovery of Zheng He (1405–33) and Polynesian peoples discovered the Pacific Islands and New Zealand. Under the patronage of Prince Henry the Navigator, the Portuguese in the 15th century sailed to the Indian Ocean, and in 1498 Vasco da Gama crossed the South Atlantic; in 1516 the Portuguese reached China. Probably with the aim of reaching the East, Christopher Columbus crossed the North Atlantic (1492) and Ferdinand Magellan found the strait which enabled him to reach the Chinese coast (1521). The North American landmass was such a deterrent that searches were long made for a navigable passage to the north of it: the search for a north-west passage led Cabot to what was probably Hudson Bay (1509) and Cartier along the St Lawrence River (1534–41). North America's interior began to be explored in the 17th century, but it was not until about 1730 that the Rocky Mountains were discovered, and the continent was not crossed until 1793, when Mackenzie traversed Canada. The United States was first crossed by Lewis and Clark, in 1803. His previous scientific research helped Captain James Cook secure backing from the Royal Society for his voyages to New Zealand and eastern Australia (1769–77). The exploration and mapping of the interiors of continents continued throughout the 19th century and often accompanied colonialism.