**Pythagoras** (6th century BC)

Realized the earth was a sphere and established the numeral basis of musical harmonics.

**Empedocles** (c. 490-430 BC)

Held that all matter consisted of four elements.

**Democritus** (c.460-370 BC) and **Leucippus** (5^{th} century BC)

Suggested that matter was made up of extremely small, identical, invisible particles called atoms.

**Hippocrates** (c.460-c.377 BC)

Became known as ‘the father of medicine’.

**Euclid** (fl.c.300 BC)

Set out the principles of geometry.

**Aristarchos of Samos** (c.310-230 BC)

Realized that the earth rotates about its own axis and orbits the Sun.

**Archimedes** (c.287-c.212 BC)

Pioneered the field of mechanics and invented many ingenious devices.

**Eratosthenes of Cyrene** (c.276-c.194 BC)

Calculated the circumference of the Earth with a creditable degree of accuracy.

*Source: World History, 50 key milestones by Ian Crofton*

*Source: Wikipedia*

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