Leonardo kept notebooks of his research into science, biology, anatomy, engineering and art. He was particularly keen on flying machines, and came up with a design for a type of helicopter, although it was never built.
The books were filled with drawings and diagrams, and covered with notes written in mirror handwriting. He kept them for the rest of his life.
Leonardo's major artistic achievement at this time was his depiction of 'The Last Supper', which he painted for the wall of the refectory of Santa Maria della Grazie, Milan. 'The Last Supper' perfectly illustrates Leonardo's belief that poses, gestures and facial expressions should reflect the 'motions of the mind'.
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