Platonism was originally expressed in the dialogues of Plato, in which the figure of Socrates is used to expound certain doctrines, that may or may not be similar to the thought of the historical Socrates, Plato's master. Plato delivered his lectures at the Academy, a precinct containing a sacred grove outside the walls of Athens. The school continued there long after Plato's death. There were three periods: the Old, Middle, and New Academy. The chief figures in the Old Academy were Speusippus (Plato's nephew), who succeeded him as the head of the school (until 339 BC), and Xenocrates (until 313 BC). Both of them sought to fuse Pythagorean speculations on number with Plato's theory of forms.