Vesalius did what no authority had dared for a millennium: he placed his own hands in the body and trusted what he found there over what the books had told him. The result, the Fabrica of 1543, is at once a work of science and one of the most beautiful books ever printed.
By demonstrating that Galen had described the bodies of animals and not of men, Vesalius did not merely correct a catalogue of errors — he established that nature, and not the ancients, is the final court of appeal.