It is a work titled On the Structure of the Human Body, written by Belgian physician and professor Andreas Vesalius (1514–1564) and published in 1543, when he was in his late twenties. Like other anatomists during the Renaissance (1350–1600), Vesalius conducted numerous dissections of human cadavers. Publishing his findings and drawings, his textbook soon became the authoritative reference, overturning the works of Greek physician Galen (129–c. 199).