The story goes that the Pope was requesting Leonardo da Vinci to submit some of his work for a competition for a new commission. Leonardo kept putting him off, saying he was too busy, as the requests grew more and more insistent. In the end, to avoid the Pope having him arrested, he drew, freehand, at arms length, a perfect circle on a sheet of paper and sent it to the Pope, who promptly gave him the commission. The reason for this is that to draw a perfect circle, freehand and unsupported is one of the hardest things possible to draw, achieved by few artists, usually only after much practice and was for a long time considered to be the pinnacle of artistic achievement.