On June 24, 1490, Leonardo da Vinci had dinner with another artist, Giacomo Andrea, to discuss the "Vitruvian Man". Andrea showed da Vinci his sketches, which would provide a foundation for da Vinci's drawing. Some time after, da Vinci finished his own famous sketch, illustrating the perfects proportions of the human body. This sketch also has many religious and mathematical implications. 

Source: Isaacson, Walter. “Vitruvian Man”. Leonardo Da Vinci. Simon & Schuster, 2017.

Photo Source: https://commons.wikimedia.org/wiki/File:Da_Vinci_Vitruve_Luc_Viatour.jpg