Once out on the open sea, however, mariners could depend on the sky to tell them where they were. Aside from announcing seasons, the proximity of land, and the weather, the sky signaled location and direction: where the boat was and where it should be heading. In other words, the sky transformed wayfinding into navigation, the “haven-finding art”3—valued greatly in Europe by the late sixteenth century, when a mathematics-minded instrument maker in Antwerp penned this definition:
This art is divided into two, namely common navigation and grand navigation. . . . The whole science of common navigation is nothing more than knowing perfectly by sight all capes, ports, and rivers, how they appear from the sea, what distance lies between them, and what is the course from one to another; also in knowing the bearing of the moon on which high and low tides occur, the ebb and flow of the waters, the depth, and the nature of the bottom. . . . Grand navigation, on the other hand, employs, besides the above-mentioned practices, several other very ingenious rules and instruments derived from the art of Astronomy and Cosmography.4
A century later, John Seller, Hydrographer in Ordinary to several British kings—the nation’s official surveyor of rivers, lakes, and seas—described navigation as “guiding the ship in her Course through the Immense Ocean to any part of the known World; which cannot be done unless it be determined in what place the Ship is at all times.”5 And indeed, by his day, the immensity of both Ocean and World were well known. Travel books, both factual and fanciful, were perennial best sellers. Owing to a potent combination of astronomy, mathematics, cartography, literacy, weaponry, instrumentation, navigation, and intimidation, Ocean and World had been discovered, explored, charted, inventoried, fictionalized, bought, sold, colonized, grabbed, planted, harvested, and mined, and many millions of the residents forcibly Christianized or enslaved.
But there’s a backstory.
To determine the precise location of his ship, the early navigator needed reliable objects against which to compare his position. But even on a given stretch of sea, a feature that was there in the spring might be absent in the fall. And because the navigator was moving rather than stationary, sailing rather than standing, the reliability factor changed month to month, week to week, even day to day.
Since Earth goes around the Sun once a year, a stargazer looking upward from the same rooftop once a month at the same time of night sees a sky that has shifted westward one-twelfth of 360 degrees, or thirty degrees, from the previous month’s sky. Early astronomers tracked this cycle carefully. Shangshu, or The Book of History, written in China in the first millennium BC, states that Taurus rises in the east in the Sixth Month (of the Chinese year), reaches its zenith in the Eighth Month, and sets in the west in the Tenth Month—all, implicitly, at the same hour of night. Kitab al-Fawa’id fi usul al-bahr wa-l-qawa’id, or the Book of Useful Information on the Principles and Rules of Navigation, compiled in the fifteenth century AD in what is now the United Arab Emirates, states that the bright star Canopus sets due west at dawn on the 40th day (of the Islamic year) and rises due east at dawn on the 222nd day.6
Another way to think about this cycle is that, day after day, decade after decade, a stargazer will see the same stars rise at the same point on the horizon—but they will rise four minutes earlier each day. Now, add a much smaller but very real factor to the daily four-minute and monthly thirty-degree changes: the wobble of Earth’s tilted axis of rotation, at the rate of one full revolution every 25,700 years. Discovered by the ancients, that wobble—called the precession of the equinoxes—has the effect across the centuries of shifting the stars’ positions relative to the month of the year. It also affects the North Star. In Homer’s time, that star, which today we call Polaris, stood a dozen degrees from the North Pole; in Columbus’s time it stood three and a half degrees away; in Sputnik’s time, it stood right near the pole. By about AD 15,000, as Earth keeps wobbling like a top, Polaris will sit forty-five degrees away.7
When you’re sailing the high seas, the slow, centuries-long shifting of Polaris is irrelevant. But not knowing north from east can be fatal. Direction is key. Fortunately, the Sun’s appearance, disappearance, and midday shadows, as well as the paths taken by other stars and the places from which winds of different character blow, are archetypes of directionality. For example, a bright star named Alnilam—corresponding to the center of Orion’s Belt—rises due east and sets due west. As for finding north in the Northern Hemisphere, you could look more or less to where Ursa Major, the Great Bear—with its seven bright stars, the Big Dipper8—wheels around an axis, neither ascending, culminating, nor descending. The reputedly blind bard Homer, though confused about the northern nighttime sky, knew that stellar navigation would have been important to any voyager, and so he writes that Odysseus, wishing to return home, was instructed by the nymph Calypso to keep rightward of the Great Bear, the constellation that “alone of them all never takes a bath in the Ocean.”9
Indo-European languages have long distinguished Orient (rising/east) from Occident (setting/west). The Greeks differentiated sunrise and sunset at the solstices from those at the equinoxes, creating six directions from two. The Vikings, sailing from Scandinavia into the sea, differentiated landward from oceanward: land-south and land-north were easterly directions; out-south and out-north were westerly. For early navigators in low latitudes such as the Mediterranean and the Arabian Sea, the points at which the Sun rose and set were useful direction markers year-round, whereas for the Vikings, who lived at high latitudes, those points changed too drastically from month to month to be helpful. The closer a mariner sailed to the North Pole, the harder it was to gain his bearings from the Sun or the stars, and the more he had to rely on winds, birds, and tides, though he could consult Polaris as a reliable rough indicator of north. Pacific Islanders took another tack. Voyaging across Oceania, they steered their course by kavengas, or star paths: arcs described by the successive risings or settings of a series of familiar stars. These arcs would guide them from one known island to another.10
Three, four, and five millennia ago, large numbers of slow, big-bellied merchant ships crisscrossed the Old World waterways, carrying both luxuries and necessities.11 But merchants had neither the seas nor the harbors to themselves. By 2400 BC Egyptian armies were being ferried to what is now the coast of Lebanon. By 2000 BC the first true maritime power of the Mediterranean—the Minoans, inhabitants of the island of Crete—had built itself a navy. By 1300 BC fleets of marauding northerners were seizing ships and blockading naval bases that the pharaoh Thutmose III had established along the Lebanese coast.
From the earliest centuries of maritime commerce, writes the historian Lionel Casson, “the freighter had to share the seas with the man-of-war.”12 Piracy, plunder, and the taking of slaves increased in direct proportion to trade, travel, and the taking of land. Seaborne raids on both vessels and coastal settlements became commonplace; sea battles increased in scale and complexity. Meanwhile, the hunger for foreign goods mounted. Athens’ “Achilles’ heel,” exploited in war by both Sparta and Macedon, was its dependence on grain shipped from Egypt, Sicily, and southern Russia.
An amazing range and quantity of cargo was carried across the seas in ancient times. In the third millennium BC, South Asian gold, ivory, carnelian, and lapis lazuli, Lebanese cedar, and Omani and Cypriot copper changed hands at the eastern Mediterranean port of Byblos, at the Persian Gulf port of Bahrain, and at the mouths of the Indus River. Frankincense and myrrh from the Horn of Africa were ferried up the Red Sea to Egypt; lapis lazuli from Harappan settlements in the Indus Valley also made its way to Egypt. Fragments of Indian teak appear in the ruins of the Sumerian city of Ur; Minoan craftsmen worked amber from the Baltic; Mycenean jars arrived at the palace of the pharaoh Akhenaten; Chinese silk was woven into the hair of Egyptian mummies; Sri Lankan cinnamon bark scented the women of Arabia; Zimbabwean gold crossed the Indian Ocean long before Europeans staked claims in southern Africa; Han Chinese rulers had such need of war horses tha
t they imported the beasts both by land and by sea. Each year, freighters transported hundreds of tons of wheat, olive oil, marble, and herb-laden fish sauce to Athens, to Rome, to Alexandria. Local versions of fermented shrimp paste, a staple condiment in the cuisines of Southeast Asia, made their way across the South China Sea. A single merchant vessel wrecked in the first century BC near Albenga, on the Italian coast between Genoa and Monaco, held between 11,000 and 13,500 amphorae of wine.13
The Bronze Age made tin a prized commodity. Generally an alloy of copper and tin, bronze was a brilliant invention, a strong, corrosion-resistant material that could be cast at relatively low temperatures into weapons, ritual vessels, ornaments, statues, and tools. The intimidating rams at the prows of the warships that kept the seas open for the merchant ships were made of bronze. But since copper and tin are rarely found in the same patch of Earth’s crust, long-distance trade was essential to their union. And since tin could fetch many times the price of copper,14 it was definitely worth a trader’s time and effort.
By the eighth century BC, the search for tin, as well as for silver and gold, had taken the Phoenicians through the Pillars of Hercules and the Strait of Gibraltar at the western exit from the Mediterranean and onward to the Atlantic side of the Iberian peninsula, to an area called Tartessos.15 Some tin could be extracted locally there, but much more was transported overland from major sources farther north, including Cornwall, the southwestern tip of Britain, to which Herodotus seems to have been referring when he wrote in the mid-fifth century BC of the “Tin Islands, whence the tin comes which we use.” To Herodotus, those places, unglimpsed by him and everyone he’d ever met, were “the ends of the earth.” One reason none of his acquaintances had seen those sources of tin firsthand was that the navy of Carthage, the strong North African colony planted by the Phoenicians, had blockaded the Strait of Gibraltar. Nevertheless, little more than a century after Herodotus wrote those words, a daring Greek from Massalia named Pytheas may well have made his way to the Atlantic Ocean, the tin works of Cornwall, and much else besides.16
Massalia (Marseille) was the colony of a colony, one of many Greek and Phoenician maritime cities that sprouted across and beyond the full breadth of the Mediterranean from the early to the middle of the first millennium BC. During those centuries, the founding of colonies and the forging of trade routes proceeded hand in hand with the development of warships and the establishment of navies.17 Alongside all that commerce and conflict, inquiry and learning flourished as well. Interchange took place on every coast; information poured in from every direction. Anaximander, a resident of the thriving Greek city of Miletus, drew the first map of the inhabited regions of Earth. Soon afterward, Hecataeus of Miletus improved upon Anaximander’s map and produced a comprehensive geography of the known world: a doughnut-shaped collage of landmasses, a flat map of a flat Earth, with the Medi-terranean (literally, “Middle Earth”) at its heart and the continuous Ocean at its outer boundary. Soon after that, a globetrotting mathematician-astronomer named Eudoxus of Cnidus wrote his own work of geography and also devised a model of planetary motion, presenting it as an interconnected system of twenty-seven spheres, each of which rotated on an axis that passed through the center of Earth.
Pytheas thus came of age in a cosmopolitan, contentious, intellectually active world that grew larger, more acquisitive, and more fact-hungry by the day. How he got past the Pillars of Hercules is much debated; that he did so is generally accepted, as is the contention that he saw Cornwall and followed the west coast of Britain north to the Orkney Islands, with a stopover at the Isle of Man. What some scholars do dispute is whether Pytheas himself then voyaged six days north to a place the ancients called Thule (which might be Iceland) and thence almost up to the Arctic Circle.18
Let us be believers. Let us say Pytheas did all the things his advocates say he did. So, during his voyage, besides searching out tin, he periodically measured the height of the Sun; recorded the shadows cast by a gnomon at various locations; gasped at the prodigious tides of the Pentland Firth; counted the number of islands in the Orkney group; and took note of the houses, crops, and beverages of the communities he visited. In Thule, at the outskirts of the Arctic Circle, he witnessed extreme phenomena: “the place where the sun lies down [and] straightaway rises again” and the “Congealed Sea” lying one day’s journey from land, a region “where neither earth was in existence by itself nor sea nor vapor, but instead a sort of mixture of these . . . [where] the earth and the sea and all things are together suspended, . . . existing in a form impassable by foot or ship.” From Thule he traveled east in search of amber and then south, completing his circumnavigation of Prettanikē (whence “Britannia”) and masterfully approximating its rough perimeter as the equivalent of 4,400 modern miles.19 Upon returning to Massalia he wrote a periplus (“sailing around”), a treatise called On the Ocean, of which not a single copy survives—only respectful paraphrases and skeptical dismissals.20 Pytheas wasn’t the first Mediterranean mariner who reputedly entered the North Atlantic; he was just more adventurous and science-minded than his predecessors.
Traditionally, the conceptual universes of navigators and scholars did not overlap. Seafarers had little truck with scientists’ determinations, nor did scientists with seafarers’ findings. But Pytheas’s data were used by astronomers and geographers for centuries after his death and became as useful to plunderers and conquerors as to merchants and diplomats. Hipparchus—the mathematician-astronomer who developed the framework of degrees, parallels, and meridians that is still used to describe latitude and longitude—translated into degrees of latitude Pytheas’s careful measurements of gnomon shadows, hours of daylight, solar altitudes, and distances traveled. That’s how we know that Pytheas placed Massalia at 43° 3' N (he was only a fourth of a degree off) and paused on his northward journey at 48° 40' N (northwestern Brittany, likely the island of Ushant in the English Channel), 54° 14' N (the Isle of Man), 58° 13' N (the island of Lewis in the Outer Hebrides), about 61° (the Shetlands), and about 66° (northern Iceland).21 Hipparchus, no mean authority himself, invoked the authority of Pytheas when correcting other scientists’ blunders:
Indeed, concerning the north pole, Eudoxus . . . certainly doesn’t know what he is talking about when he says, “There is a certain star remaining always at the same place; this star is the pole of the cosmos,” since no single star lies at the pole, but an empty place [instead], near which lie three stars. The spot marking the pole, aided by these [stars] encloses a figure very nearly resembling a quadrilateral—exactly, in fact, as Pytheas the Massaliote says.22
Ambitious early wayfinders reputedly also went in the other direction: south. One voyage, a several-year clockwise circumnavigation of Africa undertaken by Phoenician mariners in about 600 BC, was initiated at the behest of the military-minded Egyptian king Necho II. A century or more later, Hanno, the king of Carthage, took a counterclockwise route with many thousands of colonists and great numbers of vessels. How far did those voyages get? Hard to say for sure.23
Hipparchus’s 360-degree system of latitude and longitude, and the calculations it made possible, gave a big boost to the sciences of geography, cartography, and astronomy. The terms “latitude” and “longitude” derive from the Greek for “breadth” and “length,” respectively, denoting a binary directionality in early maps of the known world. But the difference between the two goes very deep. The American historian Dava Sobel describes it this way:
The zero-degree parallel of latitude is fixed by the laws of nature, while the zero-degree meridian of longitude shifts like the sands of time. This difference makes finding latitude child’s play, and turns the determination of longitude, especially at sea, into an adult dilemma—one that stumped the wisest minds of the world for the better part of human history.24
Though Polaris was not yet in place to serve as a convenient North Star, the Greeks understood that if the same star or stars barely skimmed the horizon in two different cities, those ci
ties lay at the same latitude. Latitude could be calculated from the highest altitude reached by certain catalogued stars. One that could be consulted alone or as part of a pair was Canopus, a bright southern star known in Arabic as Suhail. Eudoxus knew that Canopus–Suhail could barely be seen in Rhodes but hit an angle of 7½ degrees in Alexandria. The medieval Arab navigator-poet Ahmad ibn Mājid, who measured both in degrees and in isba (the width of the knuckle of the middle finger, held at arm’s length against the horizon), advised his readers that when the star Aldebaran reached its highest ascent, the angle of Suhail would be six degrees in Sindabūr (present-day Goa) and 7¾ isba at Cape Madraka in present-day Oman. “The best method of measuring latitudes is using Suhail,” wrote ibn Mājid, “and another like this will never be seen throughout all eternity.”25
Eternity is a long time. In fact, it would take fewer than a thousand years for Polaris to elbow Suhail aside and become the present century’s best tool for finding latitude. Everywhere north of the equator, the elevation of Polaris above the horizon will currently locate you within a degree of your actual latitude on Earth.
The bright southern star Sulbār (also called Achernar, Arabic for “end of the river”) served as another reference point for calculations of latitude; according to ibn Mājid, the mu‘allim (“navigators”) who spent weeks crossing the Indian Ocean in tandem with the monsoons relied heavily on it:
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