The cadenza soon became not only a display o f execution, but
also a test o f invention. What began as an impromptu display was repeated consistently
by busy performers, and thus convinced composers to include their own written cadenzas.
Mozart composed a number o f cadenzas, and Beethoven published a book o f cadenzas
for use with his piano concertos. Sheppard summarizes the requirements o f the cadenza
in the following manner: