Imagine writing a book so influential it becomes the undisputed authority on the nature of the universe for the next 14 centuries. Now, imagine its core premise is completely wrong. That's the legacy of Claudius Ptolemy. In this episode, we're exploring the ancient world's ultimate spreadsheet guy. Ptolemy didn't just guess that the Earth was the centre of the cosmos; he built a stunningly complex and predictive mathematical model to prove it; a system of circles-on-circles that could accurately chart the strange, looping paths of the planets. We'll follow his influence from the library of Alexandria to the courts of Islamic scholars and the universities of Renaissance Europe. We'll look at his world maps that inspired Columbus (for better or worse) and his theorems that enabled modern trigonometry. This is the story about the power of a useful idea and why, in the history of maths, being right isn't always the most important thing.