By 335 he had returned to Athens, starting his own school there known as the Lyceum. Aristotle taught courses at the school for the next twelve years. It is during this period in Athens from 335 to 323 when Aristotle is believed to have written many of his works. Aristotle wrote many dialogues, only fragments of which survived. The works that have survived are in fairly rough form. They are generally thought to be lecture notes for his students.