At about the age of eighteen, he went to Athens to continue his education at Plato's Academy. Aristotle remained at the academy for nearly twenty years, not leaving until after Plato's death in 347 BC. He then traveled with Xenocrates to Asia Minor. While in Asia, Aristotle traveled with Theophrastus to the island of Lesbos, where they researched the botany and zoology of the island. Soon after Hermias' death, Aristotle was invited by Philip II of Macedon to become the tutor to his son Alexander the Great in 343 B.C.