Eratosthenes of Cyrene (275-194 B.C.) scientific writer, astronomer, geographer and poet, he 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 Euclidean geometry.
Eratosthenes was the third librarian at Alexandria; in addition to his knowledge in many different areas, he was an accomplished mapmaker. Eratosthenes also made a catalogue of stars with 675 stars listed in it.
His followers called him the second Plato.
He was, indeed, recognised by his contemporaries as a man of great distinction in all branches of knowledge, though in each subject he just fell short of the highest place. On the latter ground he was called Beta, and another nickname applied to him, Pentathlos, has the same implication, representing as it does an all-round athlete who was not the first runner or wrestler but took the second prize in these contests as well as others. 
Eratosthenes died in 194 BC in Alexandria, Egypt.
- Is the Earth Flat? Test It for Yourself. This link describes a modern version of the Eratosthenes proof.
- Thomas Little Heath, A History of Greek Mathematics (2 vols.) (Oxford, 1921).