The spherical shape of the Earth was already known in ancient Greece, as a result of the observations and experiments carried out by Eratosthenes in the III century before christ. Furthermore, he was able to measure the length and radius of the planet with an error between 1-10%. However, an anti scientific movement has spread around the world in the last few years, defending that the prooves stating the shape of the Earth are not clear and the spherical-Earth theory is some kind of conspiracy of governments, scientists and space agencies. This project aims to prove otherwise using the methods available in Eratosthenes times. In addition, the development of scientific knowledge in ancient greek will be studied, focusing on Eratosthenes and the Alexandria library. A multidisciplinary approach will be followed involving several subjects: Mathematics, Scientific Culture, Physics, Philosophy, Geography, History and/or Greek, apart from English and French.