Eratosthenes of Cyrene was the chief librarian at the Library of Alexandria. He is best known for being the first person to calculate the circumference of the Earth. He did it by measuring Sun's angle of elevation at noon on the solstice in Alexandria, knowing, that at the same time the Sun is at Zenith in the Ancient Egyptian city of Swenet, 5000 stades from Alexandria. Seventeen hundred years after Christopher Columbus studied Eratosthenes writings and decided that the calculations were wrong, and the Earth must be smaller - which led him to seek India in the west.