Ancient science — Presocratics, Aristotle, Euclid, Archimedes, Ptolemy, Galen
Anchor (Master): Lloyd 1970/1973; Neugebauer, O., The Exact Sciences in Antiquity (1952/1969); Netz, R., A New History of Greek Mathematics (Cambridge, 2022); Sarton, G., Introduction to the History of Science (1927); Cuomo, S., Ancient Mathematics (Routledge, 2001)
Intuition Beginner
Long before the scientific revolution, the Greeks built mathematics, astronomy, and medicine that lasted for two thousand years. Between roughly 600 BCE and 200 CE, a chain of thinkers — Thales, Aristotle, Euclid, Archimedes, Ptolemy, Galen — constructed systems so coherent that they defined what counted as rigorous knowledge for the next two millennia. Their work was mathematically rich. What it lacked was the experimental method.
The distinctive Greek move was to demand that knowledge be deduced from principles rather than handed down by authority. Euclid's Elements opens with a handful of axioms and derives over four hundred propositions step by step. Archimedes weighed shapes on an imaginary lever, squeezed circles between polygons, and pinned the value of pi between two tight fractions. Eratosthenes measured the Earth from the shadow of a single pole. These were proofs, not guesses.
Yet the same tradition also held science back. Aristotle's physics — heavier objects fall faster, each element seeks its natural place — was deduced rather than tested, and it dominated for nearly two millennia precisely because it was so systematic. Galen's anatomy, drawn mostly from animals, was taught unchanged for fifteen centuries. The lesson of ancient science is that mathematics and logic can build a world-picture that endures — and that a world-picture can be both beautiful and wrong.
Visual Beginner
The table below lists the principal figures of ancient Greek and Hellenistic science with their dates and the signature quantitative result each contributes. Read it as a timeline running from Aristotle in Athens to Galen in the Roman world.
| Figure | Date | Domain | Signature quantitative result |
|---|---|---|---|
| Aristotle | c. 330 BCE | Natural philosophy | Four causes; geocentric cosmos of four elements |
| Euclid | c. 300 BCE | Mathematics | 13 books of the Elements; about 465 propositions |
| Archimedes | c. 250 BCE | Mathematics and mechanics | ; the lever law; buoyancy |
| Eratosthenes | c. 240 BCE | Geodesy | Earth's circumference stadia |
| Hipparchus | c. 150 BCE | Astronomy | Star catalogue; precession of the equinoxes |
| Ptolemy | c. 150 CE | Astronomy | Almagest; 1,022-star catalogue; epicyclic model |
| Galen | c. 170 CE | Medicine | Systematic physiology (taught for fifteen centuries) |
The key geometric fact — that the central angle alpha equals the shadow angle beta — is what lets a single surface measurement fix the whole circumference.
Worked example Beginner
Eratosthenes, librarian at Alexandria around 240 BCE, measured the circumference of the Earth using two observations and one assumption.
Step 1. Travellers reported that at Syene (modern Aswan), at noon on the summer solstice, the sun shone straight down a deep well — it was directly overhead. At Alexandria, on the same day, Eratosthenes measured the noon shadow of a vertical pole and found the sun was of a full circle, or degrees, away from overhead.
Step 2. The sun is so far away that its rays arrive parallel. By the geometry of parallel lines, the angle the sun's ray makes at Alexandria equals the angle at the Earth's centre between Alexandria and Syene. So the arc from Alexandria to Syene is of the full circle of the Earth.
Step 3. The overland distance from Alexandria to Syene was surveyed at about stadia. If of the circumference is stadia, the full circumference is stadia.
Step 4. Using the common Egyptian stadium of about 160 metres, stadia is about km. The modern value for the Earth's circumference is about km. Eratosthenes was within about two percent, using a well, a pole, and an assumption about parallel rays.
What this tells us: a single geometric idea, applied to two measurements, gave the size of the planet eighteen centuries before anyone sailed around it.
Check your understanding Beginner
Formal definition Intermediate+
Five formal structures organise ancient Greek science. Each admits a modern reformulation that exposes both its power and its limits, and each is reconstructed here in greater depth than the overview unit 33.01.01.
Axiomatic method (Euclid, c. 300 BCE). A deductive system is a tuple : a formal language of primitive terms and definitions; a set of postulates asserted without proof; a set of common notions (logical axioms such as "things equal to the same thing are equal to one another"); a collection of inference rules; and the theorems , defined as the closure of under . The Elements fixes as five geometric postulates and as five common notions; then contains the 465 propositions that follow across thirteen books. The architecture, not the specific geometric content, is the bequest: replace with Zermelo–Fraenkel set theory and the same tuple describes twentieth-century foundations [42.*].
The four causes (Aristotle, c. 330 BCE). A complete explanation of a natural thing specifies four aspects: the material cause (the matter it is made of), the formal cause (its structure or essence), the efficient cause (what brings it into being), and the final cause (its end or purpose, telos). For a bronze statue: material = bronze, formal = the sculptor's design, efficient = the act of sculpting, final = to honour the subject. Aristotle treats final causes as real and indispensable, above all in biology. Modern physical science retains only the efficient cause, with the material cause in attenuated form; final causes survive in biology solely as shorthand for natural selection [18., 19.].
The method of exhaustion (Eudoxus, c. 370 BCE; Archimedes, c. 250 BCE). To measure a curved magnitude , construct two sequences of polygonal magnitudes with for every , and such that for each preassigned bound there exists with . Then is determined. The Greeks proved the determination by a double reductio: if the curved magnitude exceeded the proposed value, an inscribed polygon close enough would contradict the assumed inequality, and a circumscribed polygon settles the reverse inequality. The modern epsilon–limit definition of the integral (Cauchy, 1823; Riemann, 1854; [02.*]) replaces the reductio by an explicit limit object and a summation operator, which is precisely what the Greek form lacks.
The law of the lever (Archimedes, c. 250 BCE). Two weights placed at perpendicular distances from a fulcrum balance if and only if . Archimedes proves this in On the Equilibrium of Planes Book I from postulates about the centre of mass of commensurable magnitudes; it is the first quantitative law of mechanics in history and the foundation of all statics.
The geocentric two-sphere construction (Ptolemy, c. 150 CE). Place Earth at a point . For each planet choose a deferent: a circle of radius whose centre is displaced from by an offset . Choose an epicycle: a circle of radius whose centre rides on the deferent; the planet sits on the epicycle. The motion of along the deferent is uniform, not about but about a distinct point (the equant) chosen so that the angular velocity of about is constant. The planet's position is the composition
Tuning , , , and the two angular speeds reproduces the observed retrograde loops of the planets against the fixed stars. The Almagest fits each planet with such a device and catalogues 1,022 stars in Books VII–VIII.
Counterexamples to common slips
- Eratosthenes did not assume the Earth is a sphere. He used the spherical-Earth hypothesis — already established by the Pythagoreans and Aristotle from the shape of Earth's shadow on the Moon during lunar eclipses — and turned it into a measurement. The novelty is the measurement, not the shape.
- The method of exhaustion is not the integral calculus. It lacks an explicit limit concept and an algorithmic theory of antiderivatives; it establishes equality by reductio, not by summation. The gap is conceptual, not merely notational, which is why eighteen centuries separate Eudoxus from Newton and Leibniz.
- Ptolemy's model is not wrong because it uses epicycles. A finite sum of epicycles approximates any smooth periodic motion to arbitrary precision (a consequence of Fourier's theorem, 1822). The model's failure was empirical — it could not match Tycho Brahe's arc-minute precision — not structural.
Key derivation Intermediate+
Derivation (Eratosthenes' measurement of the Earth's circumference, c. 240 BCE). Let denote Syene and Alexandria, two points on the surface of a spherical Earth, with on the Tropic of Cancer so that at noon on the summer solstice the sun is at the zenith over . Let be the Earth's centre and let denote the central angle subtended by the arc .
Geometric step. The sun's rays arriving at and at are parallel, because the sun–Earth distance dwarfs the chord . The ray through points along the radial line (the sun is at the zenith at ). The ray through strikes a vertical pole at at an angle from the local vertical, i.e. from the radial direction . Since the rays through and are parallel, the radial directions and cut these parallel rays in the plane through and the sun; the angle at between the two radii is therefore equal to the angle at between the ray and the radius, by the alternate-interior-angle theorem. The surface measurement at Alexandria is thus a measurement of the central angle at the Earth's centre: .
Numerical step. Eratosthenes measured of a full revolution, that is, . Since , the arc is exactly of a great circle. With the surveyed overland distance stadia, the full circumference is
Eratosthenes later rounded the figure to stadia, so that one degree of arc corresponds to exactly stadia and the arithmetic divides cleanly into the circle.
Comparison with the modern value. The polar circumference of the Earth is km. The conversion from stadia to kilometres is contested because several Greek stadia coexisted (Olympic, Egyptian itinerary, Philetaerian). Using the Egyptian itinerary stadium of roughly m gives km, an error of about . Using the Olympic stadium of m gives km, an error of about . The respectable figure, sustained by most modern scholars (Fischer 1975; Russo 2004), is that Eratosthenes' working stadium was near m and his result lay within a few percent of the true value — a precision not regained in Europe until the eighteenth-century geodetic surveys.
Where the residual error lives. The two facts that make the derivation work — the parallelism of the solar rays, and the equality — were assumed rather than measured. Eratosthenes also assumed that Alexandria and Syene lay on the same meridian (they differ by about of longitude), and that Syene lay exactly on the Tropic of Cancer (it lies slightly north of it). The residual error comes almost entirely from these assumptions and from the survey of , not from the geometry, which is exact.
Bridge. Eratosthenes' derivation builds toward 33.03.01, the geodetic and astronomical programme that Copernicus, Kepler, and Newton inherit, and the central insight — that a local angular measurement determines a global curvature — appears again in 33.03.02 pending and in modern cosmology, where the angular-diameter distance to standard rulers such as baryonic-acoustic-oscillation galaxies recovers the spatial curvature of the universe. This is exactly the move that identifies a geometric relation on the sphere with a measurable quantity on its surface; the bridge is the parallel between Eratosthenes' of arc and the cosmic angular-diameter ladder; and putting these together shows why a single shadow could size a planet while a handful of standard rulers can size a cosmos.
Exercises Intermediate+
Advanced results Master
Seven named results carry the quantitative weight of Greek and Hellenistic science. Each is stated precisely enough to admit formal verification in a modern system, and each is dated to the surviving primary text in which it first appears.
1. Archimedes' bounds on . By inscribing and circumscribing regular -gons about a circle, Archimedes proved , equivalently (Measurement of a Circle, Prop. 3, c. 250 BCE) [Archimedes c.250 BCE]. The procedure is exhaustion, not estimation: the bounds are proved by polygonal perimeter inequalities, not approximated from measurement.
2. Quadrature of the parabolic segment. The area of a parabolic segment is the area of the inscribed triangle with the same base and vertex (Quadrature of the Parabola, Prop. 24). Archimedes gives two proofs: one by exhaustion, one mechanical, summing the geometric series — the first documented summation of an infinite series.
3. Area of the circle. The area of a circle equals that of a right triangle with base equal to the circumference and height equal to the radius, (Measurement of a Circle, Prop. 1). This is the exhaustion result proved in full in the Full proof set below.
4. The law of the lever. Commensurable weights at distances from a fulcrum balance if and only if (On the Equilibrium of Planes I.6). The proof proceeds from postulates on the centre of mass of symmetric systems of equal weights.
5. The Sand Reckoner. Archimedes bounded the number of sand grains required to fill the Aristotelian cosmos at no more than in modern notation (The Sand Reckoner, c. 250 BCE), inventing an exponential notation — the "orders" of myriads — to operate with numbers far exceeding the capacity of the Greek myriad-based system. This is the first known construction of a systematic large-number notation.
6. Ptolemy's chord table. The Almagest (c. 150 CE) tabulates the chord function at half-degree intervals from to with [Ptolemy c.150 CE]. The identity underlying the table, , is a dressed form of the Pythagorean identity , and the table is the historical origin of trigonometry.
7. The Hippocratic clinical method. The Hippocratic Corpus (c. 420–350 BCE) systematised prognosis by recording the day-by-day course of diseases and treating by regimen — diet, exercise, environment — rather than by temple healing. The method is separable from its erroneous humoral theory, and it is the ancestor of modern evidence-based clinical observation [35.*].
Synthesis. The architecture of Greek science is the foundational reason that, for two thousand years, to know a domain meant to axiomatise it: Euclid's axioms for space, Archimedes' postulates for the lever, Ptolemy's deferent–epicycle–equant device for the planets, the Hippocratic case-series for the body. The central insight — that a small set of principles, unfolded by deduction, generates an entire world — is exactly the structure that seventeenth-century mechanics inherits through Newton's Principia, and putting these together with Archimedes' separation of mechanical discovery from exhaustion-proof identifies the methodological DNA of modern mathematical physics. The bridge is that every result above generalises in one direction — exhaustion into the Riemann and Lebesgue integrals [02.], the lever law into the principle of moments and then Lagrangian mechanics [09.], the chord table into modern trigonometry [28.], the Hippocratic case-series into the clinical trial [35.] — while the two great failures, Aristotelian physics and Galenic physiology, appear again in 33.03.02 pending as the precise targets that Galileo, Harvey, and Newton must demolish before the modern programme can begin.
Full proof set Master
Proposition 1 (Area of the circle, Archimedes, Measurement of a Circle I). Let a circle have radius and circumference . Let be the right triangle with legs and , so that . Then the area of the circle equals .
Proof (Eudoxus–Archimedes exhaustion). Two lemmas are required. Lemma (i): the perimeter of an inscribed regular polygon is less than , and the perimeter of a circumscribed regular polygon is greater than (proved in Archimedes, On the Sphere and Cylinder I, from the postulate that of two concave curves with the same endpoints, the one enclosed contains the shorter length). Lemma (ii) is Elements X.1: given two unequal magnitudes, one can inscribe in the larger a regular polygon whose area exceeds any assigned bound below it; equivalently, the leftover area between the circle and an inscribed (or circumscribed) regular polygon can be made smaller than any preassigned magnitude by repeatedly doubling the number of sides.
The area of any regular polygon equals half its perimeter times its apothem , since the polygon is a union of congruent isosceles triangles each of height and base equal to the side length.
Suppose for contradiction that . By lemma (ii), choose an inscribed regular polygon with , so that . The apothem of an inscribed polygon satisfies , and by lemma (i) its perimeter satisfies . Hence , contradicting . Therefore .
Suppose conversely that . By lemma (ii) applied to the circumscribed figure, choose a circumscribed regular polygon with , so that . The apothem of a circumscribed polygon equals the inradius (the circle is its incircle and touches the midpoint of each side), and by lemma (i) its perimeter satisfies . Hence , contradicting . Therefore .
Combining the two inequalities gives . Substituting the circumference yields .
Proposition 2 (Law of the lever, Archimedes, On the Equilibrium of Planes I.6). Commensurable weights placed at perpendicular distances from a fulcrum balance if and only if .
Proof. Suppose in lowest terms, so that may be replaced by equal unit weights and by equal unit weights. Archimedes postulates that the centre of mass of any symmetric arrangement of equal weights lies at the geometric centre of the arrangement, and that equal weights at equal distances from the fulcrum balance. Arrange equal weights uniformly at unit spacing along the lever, centred on the fulcrum. By symmetry the whole arrangement balances. Group the weights on one side of the fulcrum and the weights on the other; the even spacing places the centre of mass of the -group at distance from the fulcrum and that of the -group at distance , and the combined centre of mass of the total weights lies at the fulcrum. Balancing moments about the fulcrum gives , which, on substituting and , is precisely . The incommensurable case extends by the method of exhaustion, treating the balance condition as a continuous function of the weight ratio.
Connections Master
Islamic and medieval preservation
33.02.01. The results of this unit reached the modern world almost entirely through the Islamic translation movement and the Latin translators of Toledo. The Almagest, the Elements, Archimedes' hydrostatics, and Galen's corpus survived in Arabic copies and entered Latin Europe in the twelfth century, where Scholastic thinkers welded Aristotelian physics to Christian theology. The depth reconstructed here is the inheritance that33.02.01carries forward.The Scientific Revolution as demolition
33.03.01. Aristotle's physics and Ptolemy's astronomy are not background context for33.03.01; they are its explicit targets. Copernicus displaces the Earth from Ptolemy's centre, Galileo's falling bodies refute Aristotle's law of motion, and Newton's three laws replace Aristotelian dynamics outright. The axiomatic method, however, is inherited rather than overthrown — Newton writes the Principia in deliberately Euclidean style.The comparative ancient setting
33.01.01. This unit deepens the Greek strand of33.01.01, which situates Mesopotamian, Greek, Chinese, and Indian science side by side. Eratosthenes' measurement and Hipparchus's star catalogue draw directly on Babylonian observational data, and the cross-cultural transmission that33.01.01maps is the precondition for every result reconstructed here.The social and political setting of Greek inquiry
32.06.02pending. Geoffrey Lloyd argues that the adversarial, public culture of the Greek polis — the assembly, the law courts, the competitive display of argument — rewarded bold deductive claims and the refutation of rivals. This unit's emphasis on proof over observation is a product of that social context, treated in the world-history chapter at32.06.02pending.Foundations and analysis [42.] and [02.]. The Euclidean axiomatic tuple is the structural ancestor of every modern foundational system [42.], and Archimedes' method of exhaustion is the direct ancestor of the Riemann and Lebesgue integrals [02.]. The Lean proof assistant used throughout this curriculum's formal units is the living descendant of the Elements' demand that knowledge proceed by declared-deduction from declared axioms.
Historical & philosophical context Master
The figures reconstructed here are dated by their surviving primary sources. Aristotle's Physics and On the Heavens, which fix the four-causal framework and the geocentric cosmos, date to roughly 330 BCE [Aristotle c.330 BCE]. Euclid's Elements was compiled in Alexandria around 300 BCE [Euclid c.300 BCE] and survives in over a hundred Greek and Arabic manuscript traditions; the standard modern edition remains Heath's 1926 translation of the thirteen books. Archimedes' Measurement of a Circle, On the Equilibrium of Planes, Quadrature of the Parabola, and On Floating Bodies date to roughly 250 BCE [Archimedes c.250 BCE]; his mechanical Method of Mechanical Theorems survives only in the Archimedes Palimpsest, overwritten in the thirteenth century and deciphered by Heiberg in 1906 and again by Netz and Noel in the early 2000s. Eratosthenes' Geographika, which contained the circumference measurement, is lost; our knowledge of it comes from Cleomedes' De motu circulari corporum caelestium (c. 200 CE) and from Strabo's Geographica. Ptolemy's Almagest dates to about 150 CE [Ptolemy c.150 CE] and his star catalogue to roughly 137 CE; Galen's principal physiological works — On the Usefulness of the Parts and On the Natural Faculties — date to about 170 CE [Galen c.170 CE].
The twentieth-century rehabilitation of this material is itself a historical episode. Otto Neugebauer's The Exact Sciences in Antiquity (1952, second edition 1969) demonstrated that Greek astronomy was built on transmitted Babylonian computational methods, dissolving the "Greek miracle" framing [Neugebauer 1952]. Geoffrey Lloyd's Early Greek Science: Thales to Aristotle (1970) and Greek Science after Aristotle (1973) reconstructed the social and argumentative context — the adversarial culture of the polis 32.06.02 pending — that rewarded deductive proof [Lloyd 1970]. Reviel Netz's A New History of Greek Mathematics (2022) and his earlier Shaping of Deduction in Greek Mathematics (1999) recover the diagram as a cognitive instrument rather than a decoration [Netz 2022]. Serafina Cuomo's Ancient Mathematics (2001) re-centres the practical and low-status craft contexts in which much of this mathematics was actually done, and George Sarton's Introduction to the History of Science (1927) remains the scaffolding on which the modern discipline was built.
Bibliography Master
@book{lloyd1970,
author = {Lloyd, G. E. R.},
title = {Early Greek Science: Thales to Aristotle},
publisher = {Chatto and Windus},
year = {1970},
address = {London},
}
@book{lloyd1973,
author = {Lloyd, G. E. R.},
title = {Greek Science after Aristotle},
publisher = {Chatto and Windus},
year = {1973},
address = {London},
}
@book{neugebauer1969,
author = {Neugebauer, Otto},
title = {The Exact Sciences in Antiquity},
edition = {2},
publisher = {Dover},
year = {1969},
address = {New York},
note = {First edition Brown University Press, 1952.},
}
@book{netz2022,
author = {Netz, Reviel},
title = {A New History of Greek Mathematics},
publisher = {Cambridge University Press},
year = {2022},
}
@book{netz1999,
author = {Netz, Reviel},
title = {The Shaping of Deduction in Greek Mathematics: A Study in Cognitive History},
publisher = {Cambridge University Press},
year = {1999},
}
@book{cuomo2001,
author = {Cuomo, Serafina},
title = {Ancient Mathematics},
publisher = {Routledge},
year = {2001},
address = {London},
}
@book{sarton1927,
author = {Sarton, George},
title = {Introduction to the History of Science, Volume I: From Homer to Omar Khayyam},
publisher = {Williams and Wilkins},
year = {1927},
address = {Baltimore},
}
@book{heath1926,
author = {Heath, Thomas L.},
title = {The Thirteen Books of Euclid's Elements},
edition = {2},
publisher = {Cambridge University Press},
year = {1926},
address = {Cambridge},
}
@book{dijksterhuis1987,
author = {Dijksterhuis, E. J.},
title = {Archimedes},
publisher = {Princeton University Press},
year = {1987},
address = {Princeton},
note = {Originally published by Munksgaard, Copenhagen, 1956; translated by C. Dikshoorn.},
}
@book{toomer1984,
author = {Toomer, G. J.},
title = {Ptolemy's Almagest},
publisher = {Duckworth},
year = {1984},
address = {London},
note = {Translation, with introduction and annotation.},
}
@book{netznoel2007,
author = {Netz, Reviel and Noel, William},
title = {The Archimedes Codex},
publisher = {Weidenfeld and Nicolson},
year = {2007},
address = {London},
}
@book{nutton2013,
author = {Nutton, Vivian},
title = {Ancient Medicine},
edition = {2},
publisher = {Routledge},
year = {2013},
address = {London},
}
@article{fischer1975,
author = {Fischer, Irene},
title = {Another Look at Eratosthenes' and Posidonius' Determinations of the Earth's Circumference},
journal = {Quarterly Journal of the Royal Astronomical Society},
volume = {16},
pages = {152--167},
year = {1975},
}
@book{russo2004,
author = {Russo, Lucio},
title = {The Forgotten Revolution: How Science Was Born in 300 BC and Why It Had to Be Reborn},
publisher = {Springer},
year = {2004},
address = {Berlin},
}