and canals and all that--so Leonardo didn't like to refuse. Cesare
Borgia had the felicity of being the son of the Pope, but the Pope
used to refer to him as his nephew--it was a habit that Popes once
had. Pope Alexander also had a daughter--by name, Lucrezia Borgia--
sister to Cesare and very much like him, for they took their
diversion in the same way.

Leonardo started in to do the work and make plans for fortifications
that should be impregnable. He looked the ground over thoroughly,
traveling on horseback, and his two servants followed him up in a
cart drawn by a bull, which Leonardo calmly explains was a "side-
wheeler."

Leonardo carried a big sketchbook, and as he made plans for
redoubts, he made notes to the effect that crows fly in flocks
without a leader, and wild ducks have a system and fly V shape, with
a leader that changes off from time to time with the privates. Also,
a waterfall runs the musical gamut, and the water might be separated
so as to play a tune. Also, the leaves turn to gold through
oxidation, and robins pair for life.

Leonardo also wrote at this time on the movements of the clouds, the
broken strata of rocks, the fertilization of flowers, the habits of
bees, and a hundred other themes which fill the library of notebooks
that he left.

Meanwhile, Cesare Borgia was getting a trifle impatient about the
building of his forts. Two years had passed when Cesare and his
father met with an accident not uncommon in those times. The
precious pair had indulged in their Borgian specialty for the