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Ptolemy and the Renaissance: 15th century

In the gradual spread of ancient Greek texts to medieval Europe, manuscripts of Ptolemy become known by 1400. His account of world geography is widely available after it is translated into Latin in 1410.

With the arrival of printing later in the century, a world map based on Ptolemy's information is a natural project for the publishers. The first printed version, done from engraved copper plates, appears in Bologna in 1477. The projection of the map is redrawn and made clearer in the 1482 German edition, printed in Ulm from wood blocks.

The Ptolemaic map shows the known world, from the Atlantic coast in the west to China and India in the east. India stretches on through what we now call Indonesia, to reach the edge of the map below China. The supposed ocean separating Europe from China and India is the unseen region behind the map.

Luckily for the story of exploration, this ocean is assumed to be relatively small (Ptolemy greatly reduces the more accurate figure for the circumference of the earth arrived at by Eratosthenes). The unseen ocean is small on the world's first globe. And it is on this same assumption that Columbus sails west, just fifteen years after the first printed edition of Ptolemy, confident that he will soon reach the coast of India or China.

Another Ptolemaic error is disproved by the explorers just a few years later. Even though Herodotus reported that a Phoenician fleet had sailed round the southern tip of Africa, the Ptolemaic map shows south Africa extending east through terra incognita to join up with India in the far East, making the Indian Ocean a vast inland sea.

In 1497 Vasco da Gama makes his way round the Cape of Good Hope, pioneering the sea route to India which he reaches in 1498. Rarely until the 20th century has new technology, in this case the printed map, been so rapidly outdated.

The first globe: 1492

One of the most unfortunate innovators in the history of invention is Martin Behaim, the creator of the world's first globe - made in Nuremberg in 1492.

His idea is excellent. A globe is the only accurate way of representing the surface of the earth. His misfortune is to base his globe on Ptolemy (who postulates a single ocean between Spain and China) and to achieve his three-dimensional version of this notion in the very year in which it is disproved - by Columbus reaching America. But Behaim shows the reason for Columbus's confidence in sailing west. The distance on his globe between Spain and China is only half what it should be.

Columbus and the Catholic monarchs: 1492

In Santa Fe, a royal encampment from which the siege of Granada is conducted, the Spanish monarchs Ferdinand and Isabella debate whether to accept a proposal put to them by a visionary explorer, Christopher Columbus.

For eight years Columbus has been pestering European courts, particularly those of Portugal and Spain, to sponsor him in an undertaking which obsesses him. The Portuguese explorers have had notable success in their attempts to sail east round Africa towards India and China, but Columbus has become convinced that he can achieve the same more easily by sailing west.

It has long been the accepted view, deriving from Ptolemy, that nothing but sea separates Europe from India and China round the back of a spherical world. During the 15th century the notion has developed that the unseen distance by sea is much less than the known distance between Europe and China by land.

Columbus believes that he has found mathematical proof of this in an apocryphal text of the Old Testament where the prophet Esdras states that the earth is six parts land to one part sea. Columbus argues, first to the king of Portugal in 1484 and then to the Spanish monarchs, that India is therefore within reach of a caravel sailing west from the Canaries.

The Portuguese court rejects his argument. The Spanish monarchs delay for years while a commission investigates his claims. Finally, in the camp near Granada, they accept his somewhat exorbitant terms regarding the honours which will be heaped upon him if he reaches India or China, and his share of whatever is found.

Once agreement is reached, after so many years, Columbus moves fast. With his partners (brothers from a Spanish ship-owning family named Pinzón) he prepares vessels for the great adventure.

Santa Maria, Pinta and Niña: 1492-1493

On 3 August 1492 a little fleet of three vessels sets sail from the small Spanish harbour of Palos. Columbus is in command of the largest, the Santa Maria; the captains of the other two, the Pinta and the NiÑa, are the brothers Martin Alonso and Vicente Yañez Pinzón.

Three weeks are spent loading stores in the Canaries until, on September 6, the three ships sail west into the unknown. During the next month there are several sightings of coastlines which turn out to be illusions. At last, on October 12, a look-out on the Pinta spies real land.

Atlantic and Pacific: 1492-1519

The Atlantic ocean begins to acquire a western edge and a definable shape after the discovery of the Caribbean by Columbus in 1492, followed by the exploration of the coast of Venezuela by a Spaniard (Alonso de Ojeda) in 1499-1500 and then landfall in Brazil in 1500 by a Portuguese navigator (Pedro Cabral).

This coastline is still believed (following the theories of Ptolemy and Columbus) to be part of Asia. That theory is not necessarily disproved by news which begins to reach the Spaniards as they make contact with the Indians of central America. The Indians speak of another sea not far away to the west.

Such a sea, if this land is indeed Asia, would consist of a huge bay somewhere south of China. It becomes known as the mar del sur ('south sea'). To be the first to find it is any explorer's dream.

An expedition to find the south sea is mounted, in a mood of urgency, by Vasco Núñez de Balboa in 1513. Balboa is the governor of a Spanish colony which he has established, in 1510, at Santa María la Antigua on the west shore of the gulf of Uraba (a region known then as Darién). He comes to believe that the south sea, with its fabled riches, could be reached from here in a fairly short expedition with a force of 1000 fighting men.

Balboa proves his point in 1513. He sets off from a Spanish colony on the Atlantic coast, in the gulf of Uraba. Four weeks later he climbs to the top of a hill and sees water to the distant horizon. He claims for the king of Spain the entire south sea, stretching away beyond the Asian promontory on which Balboa believes himself to be standing.

Somewhere in this south sea there must lie the Spice Islands, or Moluccas, already discovered by the Portuguese travelling eastwards (the first local treaties signed by the Portuguese in these islands date from 1512). The final discovery of the extent of the Pacific derives from a bold geographical theory, held by the navigator Ferdinand Magellan, as to where precisely the Moluccas might be.

Magellan's theory: 1518

Ferdinand Magellan learns the craft of navigator, between 1505 and 1512, voyaging to and around the East Indies in the service of his native Portugal. In 1516 his request for promotion is refused by the Portuguese king, who informs him that he may offer his services elsewhere.

The only alternative employment for a man of his skills is with Spain, Portugal's great rival on the oceans. As it happens, Magellan now holds a theory which could prove greatly to Spain's advantage.

The pope has granted to Spain all newly found territory lying west of the Tordesillas line, and to Portugal everything to the east of it. In terms of modern longitude, the line is approximately 50° W. In 1518 Magellan persuades the Spanish king that the spice islands, or Moluccas, may be less than half way round the globe travelling west from the Tordesillas line. If that is the case, the islands would belong to Spain.

He is almost right. The longitude of the Moluccas is about 125° E. They are therefore 185° west of the Tordesillas line, or just 5° more than half way round the globe. Spain will have a valid case, for instruments of the time cannot be so precise. But first Magellan has to reach his destination sailing westwards.

Magellan and Del Cano: 1519-1522

With a fleet of five ships, carrying 265 men, Magellan sails in September 1519 from Seville. In mid-December he reaches Rio de Janeiro. For the next ten months he explores southwards along the coast, searching for a channel through to the 'south sea' (sighted seven years earlier by Balboa).

The broad estuary of the river Plate delays him, falsely raising his hopes, and it is not until October 1520 that he begins to explore west and then south through the straits which now bear his name. The fleet is now reduced to three ships. One has been wrecked on the south American coast. The captain of another deserts and sails home from the straits.

On November 28 the three caravels begin their journey across an unknown ocean. The crossing lasts ninety-nine days, without replenishment of food or water. The explorers finally make landfall, at Guam in the Marianas, on March 6. It has been three months of nightmarish deprivation, with the crew reduced in the end to eating leather from the rigging. But the sea itself has been sufficiently friendly for Magellan to give it a name which sticks - the Pacific ocean.

The next landfall is in the Philippines.

On the island of Cebu Magellan and his party rapidly convert the ruler to Christianity, beginning a Spanish link with the Philippines which will last until 1898. But in April Magellan is killed in a skirmish with natives on the island of Mactan.

He is already west (and slightly north) of his destination in the Moluccas, and he has achieved the hardest part of the undertaking - coaxing his often mutinous crews across a vast unknown expanse of ocean. But the glory of leading the first complete circumnavigation of the globe falls to one of his officers, Juan Sebastian del Cano.

Del Cano finally reaches Spain in September 1522 with a single ship (the Victoria, only survivor of the fleet of five) and seventeen Europeans from the original crew of 265, together with four Indians. He is granted by the Spanish king, Charles V, a suitable addition to his coat of arms - the device of a globe and the inscription Primus circumdedisti me (Latin for 'you first encircled me').

With this achievement, humans at last know the extent of the planet on which we live (Copernicus, at this same moment, is beginning to think the unthinkable - that it may indeed be only a planet). But the Pacific still has surprises in store.

Problems of projection: 16th century

The European discovery of America and of the Pacific coincides with an increase in ocean travel and with the new printing techniques of woodcut and engraving. The result is a great demand for maps which can be cheaply produced and which, unlike a globe, will take little space - lying flat, and capable of being folded or even bound into book form.

The printed map is in its vigorous infancy during the 16th century. But a globe remains the only accurate way of representing the land masses on the surface of the spherical earth. How are the newly discovered facts of world geography to be represented on a flat surface?

The problem is real, and in a real sense insoluble. Imagine a rubber globe, hollow like a football. The information on its surface is accurate. But try cutting the globe in half and laying each half out flat, as on a page. It is impossible to do so. Distortion is inevitable. The particular distortion chosen is known as the map's projection. One of the best known is that used by Gerardus Mercator.

His framework is far from new. The grid system of latitude and longitude dates back to Hipparchus in the 2nd century BC, and the prime meridian (or 0° longitude) has run through the Canaries since the second century AD, placed there by Ptolemy. But Mercator's projection is based on new scientific principles.

Mercator's projection and atlas: 1569-1595

Mercator publishes in 1569 a map of the world specifically stated, in its title, to be intended as an aid to navigation. It is laid out on the projection now known by Mercator's name, though it has been used by one or two others before him.

Mercator's projection has the effect of greatly enlarging territories as they recede from the equator. India, for example, appears smaller than Tierra del Fuego. The Moghul emperor Jahangir is understandably displeased at the diminutive size of his empire when the British ambassador, Thomas Roe, presents him with a copy of Mercator's world map.

The distortion of Mercator's projection is a benefit to navigators. By gradually lengthening the lines of longitude towards the poles, Mercator achieves a matching scale for longitude and latitude in every section of the map (the northern degrees of latitude, being shorter in reality, are exaggerated on a regular grid). A compass course can be plotted at the same angle on any part of Mercator's map. As a result marine charts still use this projection.

From 1569 Mercator devotes himself to a vast project, producing a series of maps of Europe which compare Ptolemy's version with improvements based on modern knowledge (much as Vesalius has to measure his own anatomical discoveries against the yardstick of Galen).

By the time of his death Mercator has either published or prepared large engraved maps, designed for binding into volume form, of France, Germany, Italy, the Balkans and the British Isles.

A year after his death, in 1595, Mercator's son issues the entire series under the title Atlas sive Cosmographicae Meditationes ('Atlas, or cosmographic meditations'). It is the first collection to bear the title 'atlas'. Probably based on the Greek mythological character Atlas, whose task is to support the heavens, the name becomes the standard European word for a volume of maps.

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