As he walked through the storied gates of Alexandria in the fall of 1801, a young British officer named William Richard Hamilton found himself in the middle of a stunning tableau—abject misery set against the lost grandeur of the Pharaohs. Once the ancient world’s greatest center of learning, the city of Alexandria was now a burning ruin, caught in the grip of a European war played out on African land. In the wake of Britain’s crushing victory over Napoleonic France, injured soldiers lay dying in the scorching sun; prisoners freed from dungeons dragged their battered bodies through the streets; starving families fought over the last of the armies’ dead horses. To Hamilton, however, the moment was the opportunity of a lifetime. On his own, the twenty-four-year-old Cambridge-educated classicist had been sent to Egypt with a single mission: to find the Rosetta Stone.

Largely ignored for centuries by European elites schooled in the glory and languages of Greece and Rome, Egyptian culture had only recently begun to receive recognition for its astonishing achievements and even greater antiquity, making it a new and especially coveted prize for European powers obsessed by military and cultural supremacy. Three years earlier, in the summer of 1798, Napoleon Bonaparte had landed on the Egyptian coast, hoping to weaken Britain by blocking its land route to India. That conventional military objective, however, also forced open the door for a far more audacious scientific and cultural conquest. Behind his invading troops, Napoleon brought another, highly trained army—of scholars. These ambitious men from France, known as “savants,” were charged with appropriating everything they could unearth from the tombs or pry from the ground, attempting to assert French sovereignty over Egypt’s ancient culture. They measured the head of the Great Sphinx, mapped Cairo, surveyed towns, and painted everything that could not be rolled up and carried away. These men, botanists and engineers, artists and geologists, were living, as one of them excitedly wrote home, “at the center of a flaming core of reason,” and they believed that there was no greater symbol of their military and intellectual power than their seizing of the Rosetta Stone.

Although its neatly carved hieroglyphs were as yet undeciphered, the stone offered access to the spectacular mysteries that European scholars now realized were waiting for them along Egypt’s Nile River—mysteries that predated anything they understood, and that promised to rewrite everything they knew about history. The French had unearthed the forty-five-inch-tall stone two years earlier, in the summer of 1799, when Napoleon’s soldiers were trying to reinforce a crumbling, ancient fort on the west bank of the Nile, in the port of Rosetta. His officers immediately recognized that the dark gray slab was an object of extraordinary value, what scholars spent lifetimes hoping to find. On its face was etched a two-thousand-year-old decree written in three different languages: two unknown—Demotic, once the everyday language of the Egyptian people, and hieroglyphs, the tantalizingly mysterious language of its priests—and one known: ancient Greek, which had the power to unlock the other two. News of the find had spread quickly, and scholars and scientists throughout Europe began speaking in hushed tones of the Rosetta Stone.

That Napoleon should possess such a treasure map to ancient wisdom was intolerable to France’s imperial rival, Britain. Emerging victorious from the bloody siege of Alexandria, the British now demanded their rights as conquerors: every sarcophagus, every sculpture, every gleaming golden scarab, and, most of all, the Rosetta Stone. In defeat, hiding the stone had been France’s only remaining option, so despite its massive size—estimated at some three quarters of a ton—Napoleon’s soldiers had already moved it several times, from the fort where it was found, then to Cairo, and, finally, to Alexandria. Now it was in a warehouse, concealed in a pile of ordinary baggage and covered with mats. For the benefit of the British, the French let a rumor circulate that the stone was already gone, slipped aboard a ship leaving for Europe in the middle of the night, just as Bonaparte himself had done as soon as defeat had appeared imminent.

William Richard Hamilton, however, refused to accept such evasions. Working his way through the rubble of Alexandria, he would not believe that the Rosetta Stone had left Egypt and demanded to know where it was hidden. The commanding French general, who had personally supervised much of the cultural plunder, raged at the irritatingly determined young man, accusing the British of extorting him with “a cannon in each of my ears, and another in my mouth” and uttering a phrase that would live on as a timeless caricature of imperial double standards. “Jamais on n’a pillé le monde!” he railed scornfully—“the world had never been so pillaged!” As he knew he would, Hamilton eventually discovered the stone’s hiding place, and five months later, carried aboard the captured French frigate HMS Égyptienne, it finally reached London, where it immediately became the greatest treasure in the British Museum.

Far from quenching Europe’s interest in the mysteries of the Nile, the arrival of the Rosetta Stone fueled a decades-long obsession with Egypt, Middle Eastern cultures, and “orientalism.” By the time the stone’s hieroglyphs were finally deciphered twenty-three years later by a French scholar named Jean-François Champollion, Europe’s fascination with Egyptian history and the Nile Valley had grown into a full-scale frenzy. Once the cryptic secrets of the Pharaohs’ forgotten language were unlocked, they opened a floodgate of interest and scholarship, which in turn cascaded through popular culture. From archaeology to art, poetry to fashion, the allure of a vast, gleaming civilization lost in time proved irresistible to the public. Generations of aristocrats would devote their money and time competing to unearth new dimensions of this ancient world, and to reconcile it with the classical Greek and Roman texts and history they had been steeped in from their first days in school. Among the most beguiling of the stories they had read were the wide-ranging theories about the source of the Nile, from speculations by the Greek historian Herodotus to the failed expeditions of Roman emperor Nero’s elite Praetorian Guard.

Having vaulted his country to the forefront of this new trend, Hamilton, like the rest of the world, only grew more captivated by the secrets of the Nile. As his youthful features became creased with lines and his patrician chin softened with age, he intensified his study, publishing his own translation of the Greek portion of the Rosetta Stone. Adding yet another controversial cultural icon to his record, he helped retrieve the Parthenon Sculptures after one of the ships carrying them sank to the bottom of the sea. In 1830, he then helped enshrine Britain’s national preoccupation in institutional form by becoming an original member and later president of the Royal Geographical Society, even giving it its Latin motto: Ob terras reclusas—“For the discovery of lands.”

Putting its greatest minds and vast imperial fortunes behind the task of exploring humanity’s ancient roots, Britain rapidly took a leading role in the new fields that were opened up by that quest, with the Royal Geographical Society as its principal organizer and advocate. Even as it filled the British Museum with artifacts appropriated by imperial force, however, the Society’s ambitions in pursuing ancient Egypt to the headwaters of the Nile were frustrated by the sheer scale of the majestic river, the longest in the world, which defeated countless attempts to reach its origins. Standing in the way of any attempted exploration were vast uncharted territories, defended by local peoples and countless physical hardships, that were presumed to conceal the secret heritage of the entire modern world.

Rather than fighting their way upriver, which would also entail discerning which of the bewildering number of tributaries would qualify as the principal source of the Nile, explorers shifted their attention to a bold alternative plan: landing on the eastern coast of Africa, well below the equator, and proceeding inland in hopes of finding the watershed where a stream began to course northward on the four-thousand-mile journey to Egypt. This epic end-around tactic was supported by rumors of a giant lake region that was said to exist in the central part of the continent. This strategy also took advantage of Britain’s burgeoning military and naval strength, allowing the explorers to transport their supplies and equipment by sea to key ports and staging areas such as Aden and the island of Zanzibar, which lay protected by twenty miles of sea just off the coast where an expedition would need to land and start its journey inland.

By bringing British explorers into direct contact with the interior of Africa this undertaking would effectively reconnect, as DNA analysis would later prove, a culture from a more recent site of development to some of the most ancient lands where human migration first began. It thus set the stage for the “discovery” of regions that had in fact been occupied continuously by human beings for hundreds of thousands of years longer than London or Paris. As similar encounters from Hispaniola to Peru had amply proved, however, the disparity of power and resources between the two sides in such meetings was fraught with the potential for tragedy and exploitation. The consequences of that dangerous asymmetry had been demonstrated in Africa over the preceding centuries, as European, North American, and Arab traders who moved between two worlds capitalized on their power by enslaving African peoples and selling them for profit. For explorers, that wrenching injustice was as much a reality of the region as geography or climate, shaping everything from the location of ports and availability of food to the paths they would follow. In fact, their own efforts would doubtless lead to the plunder of the very land they wished to explore. As the British writer Samuel Johnson had written less than a century earlier, after the Arctic expedition of Captain Constantine Phipps, “I do not wish well to discoveries for I am always afraid they will end in conquest and robbery.”

Still, with all of Britain’s growing knowledge and imperial might, the task of searching such an unfamiliar region for the source of a faraway river was so difficult and forbidding that it remained all but impossible. By the 1850s, with Britain’s national pride engaged and the prestige of transformative scientific discovery and the plans for imperial expansion at stake, the Royal Geographical Society resolved to mount one of the most complex and demanding expeditions ever attempted. Although among its members were scientific luminaries that ranged from Charles Darwin to David Livingstone, the Society knew that this undertaking would require experience and insight that were beyond the reach of anything it had accomplished in the past. It would need the help of skilled African guides and porters, a heavy debt that was rarely acknowledged, but it would also need more than just an explorer. It would need a scientist and scholar, an artist and linguist, an extraordinarily skilled writer and an ambitious, obsessive researcher—an army of savants in a single man.