Eratosthenes (275-194 B.C.) was the first Greek mathematician to calculate the circumference of the earth and the tilting of the earth's axis during rotation. He used principles of Euclidian geometry.
He also invented the sieve of Eratosthenes, which is a technique for separating composite from prime numbers in a natural series. In addition, he was an accomplished mapmaker.
His followers called him the second Plato.