A discovery destined to rewrite a crucial chapter in the history of science has emerged from the shelves of the National Central Library of Florence. A recent inquiry unearthed a volume of extraordinary interest: a printed copy of Claudius Ptolemy's Almagest, published in Basel in 1551 and containing several manuscript additions by Galileo Galilei. A young scientist from the University of Milan made the discovery as part of a project that began almost three years ago. The aim was to clarify Galileo’s direct knowledge of the Almagest, the astronomical treatise composed in the 2nd century AD by Ptolemy and a reference point for astronomy for more than a millennium. This is more than just the rediscovery of an annotated volume; it is the reappearance of a document that explains the route that led one of modern science's founding fathers to forever transform our understanding of the universe.