What Was the Age of Exploration? How Europe Mapped the World and Changed It

The voyages were driven by trade. Spices, silk and other Asian goods reached Europe through a chain of Muslim and Italian middlemen, each taking a margin, and a direct sea route would cut them all out. The tools were in place: the compass, from China; the astrolabe and tables for finding latitude from the sun, from Arab astronomers; the caravel, a small, nimble ship with triangular sails that could beat into the wind; and printed maps and accounts of earlier travellers, including Marco Polo, which circulated widely after 1450. Gunpowder weapons gave small crews an advantage over anyone they met.

Portugal went first because it faced the Atlantic, had nowhere else to expand, and had a prince, Henry, called the Navigator, who spent forty years from about 1420 sponsoring voyages down the African coast, each one going a little further. Spain followed once it had finished the conquest of Granada in 1492.

The key journeys came in a rush around the turn of the sixteenth century:

• •1488: Bartolomeu Dias rounds the Cape of Good Hope, proving the Atlantic and Indian Oceans connect
• •1492: Christopher Columbus, seeking Asia by sailing west for Spain, reaches the Caribbean and never accepts it is not Asia
• •1498: Vasco da Gama reaches India by sea, and Portugal begins building a trading empire from Africa to Malacca
• •1500: Pedro Cabral, blown off course to India, lands in Brazil
• •1519 to 1522: Ferdinand Magellan's expedition crosses the Pacific; Magellan is killed in the Philippines and one ship of five returns, completing the first circumnavigation
• •1519 to 1533: Cortes and Pizarro conquer the Aztec and Inca empires with small forces, local allies and epidemic disease

In 1494, two years after Columbus, Spain and Portugal agreed at Tordesillas to split all newly found lands along a line 370 leagues west of the Cape Verde Islands: Portugal took everything east, Spain everything west. Nobody else was consulted, and the line, when it was extended round the globe, gave Portugal Brazil and placed the Philippines on Portugal's side, though Spain colonised them anyway. The treaty is why Brazil speaks Portuguese and the rest of South America Spanish, and it was ignored by the English, French and Dutch, who began their own voyages in the sixteenth century and their own colonies in the seventeenth.

The lasting consequence was biological. The historian Alfred Crosby named it the Columbian Exchange: for the first time since the continents separated, the plants, animals and microbes of the Old World and the New moved between them. Maize, potatoes, tomatoes, chillies, cacao, tobacco and cassava went east and transformed farming from Ireland to China; wheat, sugar, coffee, horses, cattle, pigs and sheep went west and transformed the Americas. The potato alone allowed Europe's population to grow as it had never done, and maize did the same for parts of Africa and China.

The microbes went mainly one way. The peoples of the Americas had no exposure to smallpox, measles, influenza or typhus, and within a century of contact their population had fallen by something like ninety percent, the largest demographic catastrophe on record, which is the main reason a few hundred Spaniards could take empires of millions. Syphilis appears to have travelled the other way. Sugar plantations in the emptied lands needed labour, and the Atlantic slave trade, which carried some twelve million Africans across the ocean over the following three centuries, was the direct result.

For most of the last five hundred years the voyages were told as a story of daring and discovery, and the word discovery itself has become contested, since the lands had been inhabited for tens of thousands of years and the Americas had been reached by Norse sailors around 1000. The older histories were not wrong about the daring: Magellan's crew ate rats and leather in the Pacific, and most of the men on most of the voyages did not come back. They were silent about the cost, which fell on people who had not asked to be found. Both halves are the history, and the honest account holds them together: the same two centuries connected the world and emptied a hemisphere.

European ships were not the first to cross great distances by sea. Between 1405 and 1433 the Ming admiral Zheng He led seven expeditions from China across the Indian Ocean, with fleets far larger than anything Portugal sent, reaching India, the Persian Gulf and the coast of East Africa. The voyages were diplomatic and ceremonial as much as commercial, bringing back envoys, tribute and exotic animals, including a giraffe. Then the court turned inward, the expeditions stopped and their records were neglected, so China never followed them with an overseas trading empire.

Much earlier, Polynesian navigators had settled almost every habitable island across a vast triangle of the Pacific from Hawaii to New Zealand to Easter Island, in double-hulled canoes and without instruments. They steered by the rising and setting points of stars, the direction of ocean swells, the flight of land-based birds and the clouds that build over islands still out of sight. In 1976 the voyaging canoe Hokule'a sailed from Hawaii to Tahiti using only these methods, helping to show that such crossings had been deliberate journeys rather than lucky drift.

A popular story says Columbus had to convince people who believed the Earth was flat. Educated Europeans had known it was a sphere since ancient Greek times, and the Greek scholar Eratosthenes had estimated its size remarkably well in the third century BC. The flat-earth version of the story owes a great deal to nineteenth-century writers, among them Washington Irving, whose dramatised biography of Columbus helped popularise the idea that he battled ignorant scholars. The real argument in the 1480s was not about shape at all but about size and distance.

On that question Columbus was wrong and his critics were right. He relied on a small estimate of the Earth's circumference and an exaggerated idea of how far Asia stretched eastward, so he calculated that Japan lay only a few thousand miles west of the Canary Islands. Royal advisers who doubted him thought the ocean was far too wide for any ship of the day to cross with enough food and water, and they were correct. Columbus survived only because two continents, unknown to Europe, lay in the way. His success is a reminder that a bold voyage can succeed for reasons its planner never understood.

The routes on the map were shaped by the winds as much as by ambition. Heading south along Africa was easy with the steady north-east trade winds behind you, but the same winds blocked the way home, so Portuguese captains learned to swing far out into the open Atlantic in a great arc until they met the westerlies that would carry them back to Lisbon, a manoeuvre called the volta do mar, the turn of the sea. Columbus used the same wind system: he sailed west from the Canaries with the trades and came home much further north, where the westerlies blow.

Knowing where you were was harder than knowing the way. Instruments could give a ship its latitude, but longitude, your position east or west, could not be measured reliably at sea until accurate marine clocks arrived in the eighteenth century. Navigators relied instead on dead reckoning, estimating their position from compass heading, judged speed and elapsed time, with the hours kept by turning sand glasses. A common trick was to reach the latitude of the destination first and then sail due east or west along it until land appeared, which turned a dangerous error in distance into a survivable delay.

The continents Columbus reached are not named after him. Amerigo Vespucci, a Florentine merchant and navigator, sailed along the coast of South America on voyages between about 1499 and 1502, and accounts published under his name, including a short pamphlet called Mundus Novus, New World, argued that these lands were not the edge of Asia but a separate continent unknown to the ancients. Columbus never accepted that conclusion. Some of the letters attributed to Vespucci are thought to have been embellished or partly written by others, but the idea they spread was the one that stuck.

In 1507 the German mapmaker Martin Waldseemuller and his colleague Matthias Ringmann, working at Saint-Die in Lorraine, printed a huge world map that labelled the southern landmass America, a feminine form of Amerigo's Latin name chosen to match Europa and Asia. An accompanying booklet explained the choice. Waldseemuller later dropped the name from his maps, but too late: copies had circulated widely, and in 1538 Gerardus Mercator applied it to the northern continent as well. Only one copy of the 1507 map is known to survive. It was found in a German castle in 1901 and bought by the Library of Congress, which completed the purchase in 2003.

The Age of Exploration was the period from about 1400 to 1600 in which Portuguese and Spanish ships, driven by the spice trade and equipped with the compass, the caravel and gunpowder, found sea routes around Africa to Asia, reached the Americas and circled the globe. It joined the hemispheres in the Columbian Exchange of crops and animals, and through disease, conquest and the slave trade it remade the populations of three continents.