What did cage do to the piano for his prepared piano pieces?

A prepared piano is a piano that has had its sound altered by placing objects between or on the strings. The first composer to use it extensively was John Cage, who is often credited with inventing the instrument. ... Conlon Nancarrow adapted his player pianos in a similar way, covering the hammers with metal and leather.

based on the images pictured above, the major difference between the two cathedrals: the cathedral of notre dame and the amiens cathedral, is that the cathedral of notre dame emphasizes the horizontal lines while the amiens cathedral emphasizes the vertical lines.