Leonardo da Vinci was born today, 566 years ago.

A true Renaissance man, Leonardo was not only a painter, sculptor, and writer, but also an inventor, architect, engineer, mathematician and amateur anatomist. This pen and ink drawing was his exploration of the theories about human proportions set forth by ancient Roman architect Vitruvius.

In his treatise De Architectura, Vitruvius wrote, “For if a man be placed flat on his back, with his hands and feet extended, and a pair of compasses centered at his navel, the fingers and toes of his two hands and feet will touch the circumference of a circle described therefrom. And just as the human body yields a circular outline, so too a square figure may be found from it.

”As the sketch originally appeared in a notebook, Vitruvian man sat surrounded by handwritten notes regarding its observations about human proportion