Eratosthenes of Cyrene was a Greek Mathematician, geographer, poet, astronomer, and music theorist. He was a man of learning, becoming the chief librarian at the Library of Alexandria. He invented the discipline of geography, including the terminology used today.
He is best known for being the first person to calculate the circumference of the Earth, which he did by applying a measuring system using stadia, a standard unit of measure during that time period. He was also the first to calculate the tilt of the Earth's axis with remarkable accuracy.
He create the first map of the world, incorporating parallels and meridians.
In number theory, he introduced the sieve of Eratosthenes, an efficient method of identifying prime numbers.
The son of Aglaos, Eratosthenes was born in 276 BC in Cyrene, now part of modern-day Libya. He went to Athens to further his studies. His teachers included the scholar Lysanias of Cyrene and the philosopher Ariston of Chios who had studied under Zeno, the founder of the Stoic school of philosophy. He also studied under the poet and scholar Callimachus.
Despite being a leading all-round scholar, Eratosthenes was considered to fall short of the highest rank. Heath writes:
[Eratosthenes] 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 Beat, 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.