What describes the contribution of Eratosthenes?

Euclid was the 'father' of Geometry (the mathematics concerning the Earth) and his work remained the basis of geometry for more than 2,000 years.

Eratosthenes also was active in this field and his claim to fame is that he was the first to almost exactly calculate the circumference of the Earth and the exact tilt of the axis of the Earth (so since the time of the ancient Greeks it was known that the Earth was round and all stories that Columbus' sailors were afraid that they might fall off the rim are bogus).

Archimedes is considered one the greatest geniuses of all time in the field of Mathematics. He is the man of "Eureka!" fame, the father of modern calculus, of the principle of buoyancy of objects in water, he invented the block-and-tackle system stil used today to hoist sails and heavy objects and he invented the "Archimedes screw" still used today in factories.