"De Motu animalium" is sometimes referred to in the medical literature. But who has read it? The book, originally published in Latin, seemingly constitutes the very first treatise on biomechanics. The author, Giovanni Alfonso Borelli (1608 - 1679), was professor of mathematics and physics in Pisa where he worked with Malpighi, who was professor of theoretical medicine and focused Borelli's interest on the movements of living creatures. This was the time of Galileo, Descartes, Newton and many others, when sciences exploded, sometimes leading to conflicts with religious authorities. "De Motu animalium," Borelli's life work, has two parts. In the first part, he analyses the action of the muscles, the movements of the limbs and motions of man and animals, including skating, running, jumping, swimming and flying. The second part deals with what is now called physiology, considered from the point of view of a mechanist: heart beat, blood circulation, breathing, separation of urine from the blood in the kidneys, liver function, reproduction, fatigue, thirst, hunger, fever, and so on. This work shows Borelli to be a genial precursor. He expresses his opinion as a mathematician on problems which afterwards further stimulated the curiosity and endeavours of many generations of researchers. This book will be welcomed by anybody who is interested in the working of living bodies and in the history of human knowledge.