The Hellenistic period is the brightest period in Kos' history. In the creation of the new city (366 BC) a lot of marble monuments were built such as the sanctuary of Hercules, Pandimou and Pondias Aphrodite, the Market, the Gymnasium, the Stadium, the Theatre, the Altar of Dionysus and the Acropolis.

The relics of these monuments were brought to light by the diggings of Italian archeologists. King Ptolomeos II of Egypt was born in Kos at this time. He adored Greek literature and was know as the Philadelphos. During the Hellenistic period, the island thrived economically and culturally. Kos was not only rich in agricultural and livestock products but also started developing its export trade in wine, olive oil, fruit, perfumes, silk and wool.