Euclid

Euclid taught in Alexandria around 300 BCE, under the first Ptolemy, and nothing else is known of him. The Elements, in thirteen books, gathered the geometry and number theory of the Greeks into a single deductive structure, from definitions, postulates and common notions to the proofs of the Pythagorean theorem, the infinitude of primes and the five regular solids. It was the textbook of mathematics for two thousand years and the model of what a proof is; Lincoln studied it to learn what demonstrate meant, and St. John’s freshmen still prove its propositions at the board. The remark that there is no royal road to geometry is attributed to him.