276 BC – He was a Greek mathematician, geographer and astronomer born this year in Cyrene (in modern-day Libya), but worked and died in Alexandria, capital of Ptolemaic Egypt. 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. Eratosthenes also studied under the poet and scholar Callimachus who had also been born in Cyrene. Eratosthenes then spent some years studying in Athens.
240 BC – He is credited by Cleomedes in On the Circular Motions of the Celestial Bodies with having calculated the Earth’s circumference around 240 BC, using trigonometry and knowledge of the angle of elevation of the Sun at noon in Alexandria and in the Elephantine Island near Syene (now Aswan, Egypt).
236 BC – He was appointed by Ptolemy III Euergetes I as librarian of the Alexandrian library, succeeding the first librarian, Zenodotos, in that post.
194 BC –Erastosthenes became blind, and this year, he supposedly starved himself to death.