The Vitruvian man—
“And just as the human body yields a circular outline, so too a square figure may be found from it. For if we measure the distance from the soles of the feet to the top of the head, and then apply that measure to the outstretched arms, the breadth will be found to be the same as the height, as is the case of plane surfaces which are perfectly square.”
Vitruvius, De Architectura (III.1.3)