In his Republic Plato considers grasping the unity of mathematics as the ultimate goal of the
mathematical studies in which the future philosopher-rulers must engage before they turn to
philosophy. How the unity of mathematics is supposed to be understood is not explained
however. This book argues that Plato conceives of the unity of mathematics in terms of the
mutually benefiting links between its branches just as he conceives of the unity of the state
outlined in the Republic in terms of the common benefit for all citizens. Evidence for this
view is provided by a discussion of his conception of astronomy as a propedeutic to philosophy
which can be best understood as hinting at a historically possible link between
fourth-century-BC astronomy and solid geometry. The monograph also includes a detailed
discussion of two well-known stories about Plato: not only he motivated Greek mathematicians to
solve a difficult problem in solid geometry with his interpretation of a Delphic oracle given
to the inhabitants of the island of Delos but he also posed the question which led to the
development of the astronomical theory of homocentric spheres. It is argued that these stories
are best understood as fictional episodes in Plato's life constructed from passages in his
works.
