Kos Town does not preserve one sealed “old town” from a single era. Ancient Greek and Roman remains, a medieval Knights' castle, Ottoman buildings and Italian-period civic architecture overlap around a modern island capital. That mixture is precisely the reason to explore on foot: each block reveals how earthquakes, conquest, excavation and reconstruction repeatedly changed the town.
The ancient city expanded after the synoecism of 366 BCE and became an important administrative and commercial centre. Near today's harbour, the Ancient Agora preserves part of a much larger public and sacred district. Kos's official tourism site describes the visible market zone as approximately 152 by 82 metres, with excavated areas, columns and routes extending toward the Altar of Dionysus and other urban remains.