What was missing
Ancient sailors in the Mediterranean and Near East had no magnetic compass, no sextant and no accurate clock. Magnetic compasses appear in later medieval sources, and nothing in the surviving Greek or Roman evidence suggests they had one. That did not make them helpless. They combined experience, local knowledge and careful observation, and most journeys were designed to keep risk low.
Following the coast
The simplest method was to keep land in sight. Mediterranean geography helps: high headlands, islands and mountains are visible from a long way off, and many sea crossings are short. Sailors learned landmarks, river mouths, colours of the sea bottom and the look of the shore from the water. This kind of knowledge is called pilotage, and it was handed on by experienced captains.
Written sailing directions took this further. The Greek word periplous, “sailing around”, describes a text listing ports, distances and hazards along a coast. A few survive. The best known is the Periplus of the Erythraean Sea, a first-century CE merchant’s guide to Red Sea, East African and Indian ports and the goods traded in each. Another is the account attributed to the Carthaginian Hanno, whose date and authenticity as an actual voyage record are discussed by scholars. Collections of coastal distances also survive from the Roman period. Distances in such texts are usually given in stades or days of sailing, so they are rough estimates.
Reading the stars
When out of sight of land, sailors used the heavens. Homer’s Odyssey has Odysseus steer by the Pleiades, Boötes and the Great Bear. Greek tradition held that Phoenician sailors steered by the Little Bear, which the Greeks called the “Phoenician” constellation, while Greeks themselves used the Great Bear. Neither constellation stands exactly at the celestial pole, and in the ancient world there was no bright star at the pole, so the method gave only an approximate north.
Sailors could also judge direction from where particular stars rose or set. Egyptian sky watching produced lists of stars known as decans, used for timekeeping, and the rising of bright stars such as Sirius marked the seasons. Star lore was valuable because it told sailors both direction at night and the right time of year to sail.
Winds and the weather
Winds were the engine of a sailing ship and the main reference for direction. The Greeks named several winds by compass-like direction and by character; the Tower of the Winds in Athens, traditionally dated to around the first century BCE, carries reliefs of eight of them. Sailors tied wind directions to the sunrise and sunset points of different seasons. A captain knew which wind to expect, which one would blow him off course and which one meant a storm.
Seasonality mattered. Winter storms, low cloud and short days made long crossings risky, and many writers describe a sailing season running roughly from spring to autumn. In the Indian Ocean the same idea took a more dramatic form, because the monsoon trade winds reverse seasonally and made regular round trips to India possible. Polynesian wayfinding, with its reading of swells and star paths, is a separate and highly developed tradition from the Pacific.
Other clues at sea
- Sounding lead: A weighted line, sometimes with tallow or wax on the bottom, measured depth and brought up a sample of the seabed. Herodotus describes using a sounding line off the Egyptian coast, and sailors generally used it to detect shallows near shore.
- Birds and floating debris: Flocks flying toward or away from shore at dawn or dusk hinted where land lay. A Mesopotamian flood story has the hero release birds to test for dry land, which is a literary example of the same logic.
- Water colour and swell: Changes in colour, cloud banks above islands and the pattern of waves around a coast could indicate land before it appeared.
The limits of the methods
Without instruments, estimating position involved a lot of judgement. Sailors judged speed by eye and time by the sun, so errors accumulated on long open-water passages. Ancient geographers later used latitude measured from the sun’s height and shadows, and Greek scholars such as Eratosthenes produced estimates for the size of the Earth, but these were mainly tools for scholars and mapmakers, not for ship captains.
When ships were off course, they could be lost for days. Writers record ships blown far from their route by storms, and the large number of known wrecks suggests that navigation errors, bad weather and rocky coasts were all dangers. The system worked because most voyages followed well-known routes at well-known times.