Natural Phenomena. The term Presocratic philosopher is used to describe several thinkers who lived in the late seventh through fifth centuries. They shared an interest in trying to explain natural phenomena, though many were also concerned with the nature of the gods, healing, politics, and ethics. The earliest of the Presocratics, including Thales, Anaximenes, Anaximander, and Heraclitus, lived in Ionia, and are sometimes referred to as "Ionian nature philosophers." Two philosophers, Xenophanes and Pythagoras, migrated from Ionia to Italy; these and other philosophers living in Greek colonies in Italy (therefore referred to as an "Italian" school) include Empedocles, Zeno, and Parmenides of Elea. Melissus, though he lived in Samos (native island of Pythagoras), because of his philosophical affiliations with Parmenides and Zeno, is usually grouped with the "Eleatics." Knowledge of these philosophers is rather uncertain and only fragments of most of their work remain...