. This is first of a two lectures about the ‘Plato’s mathematical anti-atomism’ concerning his cosmology. In the first part, ‘An Introduction to the Timaeus’, I will present an overview of some cosmologies in early Antiquity, beginning with Thales to Democritus, the father of the ‘atomism’. Then I will discuss what we know or can infer about their cosmology through the texts of the most known ancient atomists, Democritus (with Leucippus), Epicurus and Lucretius. According to many scientists and philosophers, among all the doctrines in the Greek and Roman Antiquity, it is the closest to modern scientific thinking. We will consider whether such an assessment is correct or it is a modern representation grounded in an anachronistic reading of the few extant Greek texts on this doctrine.