The big-swoln Ganges and the Danube rise
In thick’ning fumes, and darken half the skies.
In flames Ismenos and the Phasis roul’d,
And Tagus floating in his melted gold.
The swans, that on Cayster often try’d
Their tuneful songs, now sung their last and dy’d.
The frighted Nile ran off, and under ground
Conceal’d his head, nor can it yet be found…

The mystery of the head of the Nile — the source for the longest river in the Old World (and the longest in the world, depending on how one measures) — was to remain unsolved for almost two thousand years. Greek and especially Roman iconography depicted the Nile god, seven-channeled Neilos, but no one could figure out where he came from. Ptolemy stated that the headwaters of the Nile could be found in the "Mountains of the Moon", but most people shrugged that off as nonsense. Ovid’s claim that the head of the Nile was underground and unfindable was myth, but the idea of snow-capped mountains in equatorial Africa was simply nonsense. And that was that.

Ovid didn’t even have a guess; when his Metamorphosis told the story of story of Phaeton, the son of Helios, and his fateful joyride in his father’s blazing chariot, he gives details about the sun’s descent and the effect it had on the rivers of the ancient world:

The big-swoln Ganges and the Danube rise
In thick’ning fumes, and darken half the skies.
In flames Ismenos and the Phasis roul’d,
And Tagus floating in his melted gold.
The swans, that on Cayster often try’d
Their tuneful songs, now sung their last and dy’d.
The frighted Nile ran off, and under ground
Conceal’d his head, nor can it yet be found…

The mystery of the head of the Nile — the source for the longest river in the Old World (and the longest in the world, depending on how one measures) — was to remain unsolved for almost two thousand years. Greek and especially Roman iconography depicted the Nile god, seven-channeled Neilos, but no one could figure out where he came from. Ptolemy stated that the headwaters of the Nile could be found in the "Mountains of the Moon", but most people shrugged that off as nonsense. Ovid’s claim that the head of the Nile was underground and unfindable was myth, but the idea of snow-capped mountains in equatorial Africa was simply nonsense. And that was that. In the 1870s, in Selkirkshire, Scotland, a boy with the remarkable name of Mungo Park was born. About a hundred years earlier, Sir Thomas Browne had written (despite the naysaying of those who "have only referred it unto the providence of God, and his secret manuduction of all things unto their ends") that

the inundation of Nilus in Ægypt proceeded from the raines in Æthiopia, and the mighty source of waters falling towards the fountaines thereof…. This theory of the Ancients is since confirmed by experience of the Modernes, by Franciscus Alvarez who lived long in those parts, and left a description of Æthiopia; affirming that from the middle of June and September, there fell in his time continuall raines.

Park would not prove Browne wrong, but he would go on to be the first great English explorer of the wilds of Africa, searching to place the semi-mythical city of Timbuktu squarely on the map. Trained as a shipboard surgeon and schooled as a botanist, a trip to Sumatra and subsequent presentation to the Linnean Society of naturalists seems to have whetted his appetite for adventure. At the behest of the Royal Society, and with the assistance of a Mandingo-speaking slave named Johnson, Park navigated, rode, walked, and bribed his way into the interior of Africa to the Niger River, which no white man had ever seen. Along the way, he was captured by bandits, stranded in the middle of a war, stricken with fever, and fêted by kings. When he staggered out of the jungle, onto an American ship, and back to London, he had been gone for over two years. No one in England had expected to see him alive again. His book — part travelougue, part anthropology text, part commercial report — was a huge popular success; Park became friends with a young Walter Scott; and when the government wanted to mount a larger expedition to the Niger a few years later, there was only one man they could turn to. Park accepted the commision, departed for Africa with soldiers, equipment, and a small fortune in gold, and arrived just in time for the rainy season; determined to press on, Park and those soldiers not felled by dysentry or fever made their way down the Niger past Timbuktu in a jerry-rigged raft, only to be killed by natives near Bussa when the raft foundered. Only one member of the expedition, a slave, survived to tell the tale.

Park’s success and fame inspired a wave of imitators, many of whom were eventually organized under the auspices of the Royal Geological Society. The source of the Nile proved harder to find than the Niger, however; James Bruce had discovered the source of the Blue Nile (which Sir Thomas Browne would be gratified to know, rises in the Ethiopean highlands and flows into but is distinct from the "White Nile"), Lake Tana, in 1770, but it wasn’t until an 1856 expedition mounted by Victorian England’s greatest explorer, the author, Arabist, and libertine Sir Richard Francis Burton. One member of the expedition was a decorated soldier, John Speke. In 1857, the two reached Lake Tanganyika. Burton was too ill to continue; Speke left him at camp and made his way on to a lake as large as Ireland which he dubbed Victoria. Upon their return to England, Speke claimed that he (and he alone) was the man who had found the headwaters of the Nile. Burton, understandably nonplussed, claimed that Speke hadn’t explored enough to know for sure what he had found. And he was right; thirty years later Henry Stanley (of "Dr. Livingstone, I presume" fame), a one-time stringer for the New York Herald, made his way to the area seeking to rescue Emin Pasha, a colonial official assumed besieged by a Muslim uprising. Pasha didn’t need Stanley’s help, but one of Stanley’s African companions pointed out a curious feature: in the distance, there were mountains that seemed to be covered with salt. The Rainmakers, the Ruwenzori Mountains, usually hidden by cloud cover and protected by rain forest, were in fact covered with snow, a delicate ecosystem of icy mountains beneath the blazing equatorial sun. A trickle from the snowpack makes its way into Lake Albert, Lake Edward, Lake Albert, and Lake Victoria; it is the true source of the Nile, right where Ptolemy, born in the first century A.D., said it was. As Sir Thomas Browne wrote, "For as things unknowne seeme greater then they are, and are usually receaved with amplifications above their nature." I’m sure Ptolemy would have agreed.