On 10 August 1519, five ships set sail from Seville to a burst of cannon fire. They slipped down the Guadalquivir – the great river of Southern Spain – and headed out into the Atlantic Ocean. They were commanded by a Portuguese adventurer, Fernão de Magalhães, who had come to Spain seeking his fortune at the court of King Charles I. Rebranded as Fernando de Magellanes (Magellan), his mission was to seek the legendary Spice Islands to which the Spanish laid claim. Of the 415 men who departed that day, only 18 were destined to return.

Behind this initiative was a long chain of events. Just as Columbus had not set out to discover America, Magellan never intended to circumnavigate the world – nor indeed did he actually do so. His aim was to track spices back to their source. Cloves and nutmeg were an engine of the world economy, the most extensively traded of all commodities. For Europeans they represented riches on an unprecedented scale. A few years earlier, the Portuguese, sailing east had identified a group of tiny islands, the Moluccas, in the archipelago now called the Philippines, as the only place of earth where the most highly valued species, cloves and nutmeg, could be found. Spain, the rival, was now aiming to dispute their claim to this spice hub.

The lure of spices is very old. Four-thousand-year-old clove buds have been excavated from cities on the banks of the Euphrates, sculpted reliefs of spice fleets recorded in the Valley of the Kings. Chinese emperors in the Han dynasty required courtiers to sweeten their breath with cloves, and the Romans held spices to be olfactory portals to the divine – to scent sacrificial offerings and to waft the souls of the dead up from funeral pyres. Spices have been valued as antiseptics, analgesics and aphrodisiacs, to cheer up food and drink, as intimations of paradise. They have been instrumental in the development of long-distance trade routes by land and sea, the growth of cities and the spread of religions by the merchants who carried them. Lightweight and durable they were the first truly global commodity; the markup as they passed through many hands has been so astonishing – as much as 1000% by the time they reached Europe – that they could be worth more than their weight in gold; at times they have been a currency in their own right.

In the Middle Ages the spice trade into Europe had been resentfully in the hands of Muslim merchants and its own bullion was draining away in payment. The secrets of the sources of cloves and nutmeg were unknown. It was the rumours of lone travellers that had whetted the appetite. Marco Polo thought that cloves came from China – he must have seen whole clove branches there imported from the Moluccas – and nutmeg from Java. The Franciscan missionary Odoric of Pordenone who passed through Java in the early fourteenth century understood that they came from somewhere further east, without being able to identify the exact spot. An Italian traveller, Ludovico di Varthema, claimed to have visited the spice islands around 1505 and described the cultivation of both cloves and nutmeg. His account was quickly in printed circulation.

This heady swirl of speculation and desire was the driver of European exploration. Columbus had set out westward for the ‘Indies’ – China and Japan – to seek spices, gold and pearls. Instead, he hit the American barrier. It was only when Vasco da Gama sailed east to India and the Portuguese captured Malacca on the Malay peninsula in 1511 that they were able to identify and then sail on to the spice bearing Moluccas.

Magellan’s voyage was an epic of endurance and suffering. As the ships worked their way down the coast of South America looking for a speculative channel into the Pacific Ocean, cold, hunger and despair gripped the fleet. Magellan’s leadership style was brutal: never apologise, never explain. When a mutiny arose on what is now the coast of Argentina, he acted dramatically. Men were tortured and executed. Two were cast ashore to enjoy a lingering death as the ships sailed away. The exploration and discovery of a channel into the Pacific Ocean – the labyrinth of the Strait of Magellan – was a terrifying saga. The cold was biting, the landscape desolate and awe-inspiring. The men became fearful that they were being led to oblivion by a monomaniac. When they finally debouched into the so-called Pacific they anticipated a short voyage. No one had anticipated the extent of the new ocean. Scurvy, the lack of Vitamin C, took hold and decimated the crew as they sailed for four months across 9,500 miles of blank sea. When they landed on the islands of the Philippines Magellan was killed in an incautious attack on the indigenous people. The survivors eventually reached the Moluccas, where most were captured by the Portuguese. The eighteen who made it back under Juan Sebastián Elcano had circumnavigated the world. They were hailed as the wonder of the age, like astronauts returned from the moon.

This race for the Moluccas were destined to become the focus of intense rivalry for the spice trade. From the outset the Spanish incursion into the Moluccas – territory that the Portuguese claimed for themselves – lit the fuse of a bitter micro war between the two Iberian peoples that lasted several decades, one in which the indigenous peoples of the Moluccas were unwilling participants. Spain launched repeated expeditions from Mexico to assert their claim but the Pacific proved an intractable problem. Despite the length of the voyage it was reasonably straightforward to sail west with comfortable winds but attempts to return were repeatedly baffled. Again and again, ships were blown back to the Philippines. To the Spanish the Pacific had become a lobster pot – easy to enter, impossible to escape. Finally cracking the code of the ocean’s winds that would enable a return voyage was the work of a largely forgotten but influential figure in the development of global exploration, Andrés de Urdaneta, a Basque who accompanied one of the failed expeditions. Urdaneta spent twelve years of his life living wild in the Moluccas. He was a deep thinker about the navigational issues of his time who finally solved the problem of the Pacific winds, pioneering a route from the Philippines back to Mexico. It was a discovery of huge significance.

Henceforward it allowed people, goods, crops and ideas to travel in both directions across the ocean. The Pacific return forged a final link in the development of long-range maritime networks. Henceforward the treasure ships of Spain, the Manila galleons, made an annual voyage to Mexico with the goods of the Orient – not just spices, but the traded goods of China and Japan and the wider east – Ming pottery, ivory, silk, gold, precious stones, live animals. In return came silver from the mines of Peru and Mexico – highly desirable to China as the basis of its tax system – along with foodstuffs, new crops and genetic material. Manila became the turntable of exchange for goods from all quarters of the globe.

The competitive attempts to reach and control the Spice Islands, driven by sophisticated sailing ships, increased skills of navigation and information gathering, and fast-firing cannons, gave a definitive shape to the planet’s seas and continents. In the process Europeans proved that the world was spherical, spanned the Pacific Ocean, created Manila, the world’s first global city, and linked up the oceans – ‘the world encompassed’ in Drake’s phrase. While the great land empires of China and India remained initially largely untouched, the spice voyages created maritime empires across distances unmatched in human history and gave birth to global trade. Six crucial decades, from 1511 to 1571, from the Portuguese conquest of Malacca to the founding of Manila, constitute a defining moment in world history. They saw Europe, hungry, competitive and aggressive, shift decisively from the margins to the centre and lift Spain briefly from backwater to world power. European maritime empires would dominate the planet for half a millennium. The epic voyages and the collisions of peoples and cultures produced extraordinary and compelling stories of endurance and courage, appalling suffering, cruelty and genocide. All this would go into the political, commercial, cultural and ecological makeup of the modern world.

Roger Crowley is the author of Spice: The 16th-Century Contest that Shaped the Modern World.