Who wrote the Elements, the foundational text of classical geometry?

Euclid compiled the Elements in Alexandria around 300 BC, and it became one of the most influential books ever written. Its lasting importance is less about the individual results, many of which were already known, than about the method. Euclid began with a small number of definitions, five postulates and some common notions, then derived hundreds of propositions from them in strict logical order, with each theorem depending only on what had already been proved. That deductive structure became the template for what a mathematical argument looks like and shaped scientific and philosophical writing for two thousand years. The Elements was used as a school textbook well into the nineteenth century. Its fifth postulate, about parallel lines, always struck readers as less obvious than the rest, and centuries of failed attempts to derive it from the others eventually led mathematicians to invent consistent non-Euclidean geometries in which it does not hold.

The Elements also contains a proof that there are infinitely many prime numbers, still admired for its simplicity.