Parts of Cortona's defensive walls date to the Etruscan period, around the 4th century BC. The most visible stretch is at the western edge of the town, where huge irregular limestone blocks form the lower courses of what is otherwise a medieval and Renaissance wall.
A short walk along Via Janelli or Via Roma takes you past these massive stones. The walls are best appreciated up close — the blocks are bigger than anything the medieval town builders attempted, and were hauled here without mortar or iron tools.