My grandfather told me about this. and i haunts me as the longstanding symbol of the perfection of art. a freehand circle that is Perfect in its conception and dimension. incontestable by science and maths.
"when the Pope sent a messenger to Giotto, asking him to send a drawing to demonstrate his skill, Giotto drew, in red paint, a circle so perfect that it seemed as though it was drawn using a compass and instructed the messenger to give that to the Pope." Giorgio Vasari on Giotto Di Bondone.