Greek Geographers

History of Maps and Cartography

Course 1 · Chapter 2 · Greek Mapmakers and Ptolemy

Greek writers turned the map into a thing that could be argued over with geometry. They reasoned that the Earth is a sphere, measured it, and proposed ways to fix any place by numbers. None of their original maps survive, so what we know comes from later descriptions and copies, a point to keep in mind throughout. Names and dates are from general knowledge and flagged "check".

From Cosmology to Geography

Anaximander

A sixth-century BC thinker from Miletus is credited by later writers with drawing an early map of the world and with a model of the cosmos (check; the attribution rests on later sources).

Herodotus

In the fifth century BC he mocked maps that showed a perfectly round world with Ocean running round it, which tells us such maps were circulating (check the passage).

A spherical Earth

By the time of Aristotle in the fourth century BC the argument for a sphere rested on evidence such as the Earth's curved shadow in lunar eclipses and the changing stars seen when travelling north or south (check).

Measuring the Earth

Figure (check each)	Contribution
Pytheas of Massalia, fourth century BC	A voyager who reported a journey into the north Atlantic, with observations of the sun's height, which were used by later geographers. His own text is lost and his reliability was disputed in antiquity (check).
Eratosthenes of Cyrene, third century BC	Librarian at Alexandria, said to have estimated the Earth's circumference by comparing the sun's angle at two Egyptian places, Syene and Alexandria, a distance known by travel time. The units he used (stadia) are uncertain, so the accuracy of the result is debated (check).
Hipparchus, second century BC	Proposed fixing places by latitude and longitude drawn from astronomical observations (check what is attributed to him and what came later).
Strabo, about 20 AD	Wrote a long Geography describing the known world, which includes a critique of earlier geographers (check).

Reasoning, not instruments The method of Eratosthenes needed only a shadow, a known distance and some geometry. What the Greeks lacked was a way to measure longitude, the east-west position, which needs accurate timekeeping or shared astronomical events. For many centuries this made the east-west scale of maps much less reliable than the north-south scale (check; Chapter 7 returns to the problem).

Ptolemy and the Geography

Who. Claudius Ptolemy worked in Alexandria in the second century AD, and also wrote the astronomical Almagest (check).
What. His Geography gives instructions for drawing maps and a list of places with their coordinates, thousands of them (check the number).
Projections. He discussed ways of drawing a curved Earth on a flat sheet, which is the problem of Chapter 5.
Problems. His coordinates were often wrong, and he used a smaller Earth than Eratosthenes, which made Asia seem to stretch further east. That error mattered later (check; see Chapter 4).
Maps. The maps that accompany the text in surviving manuscripts are copies from many centuries later, and it is debated how far they reflect his own (check).

Idea	Why it mattered (check)
Coordinates for places	A map could be rebuilt from a list of numbers, and corrected place by place.
A grid of meridians and parallels	Gave a shared frame for comparing information from different sources.
Instructions for projections	Made map-making a craft with rules that others could learn.
Authority	Because the text was so thorough, later users sometimes trusted it over newer information.

What Survived and How

Loss. No Greek map of the classical period survives in the original. We rely on descriptions and on later copies (check).
Transmission. Ptolemy's work was studied in the Byzantine and Islamic worlds, and reached Latin Europe in the early fifteenth century, when it was translated and printed within decades (check dates; Chapter 4).
A caution. A "Ptolemaic map" drawn in 1480 is a Renaissance reconstruction from his text, not a map he drew.

A British comparison Ptolemy lists a Britain that is rotated, with Scotland bent to run east-west, a mistake that appears on printed maps as late as the sixteenth century (check). It is a handy example of how an authoritative error persists until a new survey replaces it, which Chapter 6 shows for Scotland itself.

Check the details Eratosthenes' figures depend on the length of a stadion, and the "very accurate" claim often repeated needs care. Attributions to Anaximander and Hipparchus rest on later writers. Check the sources before quoting any number.

Exercises

Exercise 1

Explain in your own words how Eratosthenes' method works, and list the assumptions it relies on.

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Exercise 2

Why is it misleading to speak of "Ptolemy's map of the world"? Write a more careful sentence.

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Exercise 3

Explain why an error in the size of the Earth could change a plan for a voyage.

→ Solution

Quick Reference

Eratosthenes: measured the Earth by shadow angles (units uncertain)
Hipparchus: latitude and longitude from astronomy
Ptolemy: Geography, coordinates and projections
Survival: originals lost, later copies and reconstructions
Weak point: longitude, and a too-small Earth