Geometry reached its mature form around 300 BC, when Euclid connected all proofs that had been developed up to that point and showed they could al be derived from just 5 self-evident assumptions, known as axioms.
One of the axioms, for instance, tells us we can always connect two point with a line. Who could doubt that? Accepting the axioms, logic makes it necessary that the all of Euclids theorems are also correct.
"The Great World History Book"