Kefalonia was populated during the 10th millennium B.C. She was separated into four  autonomous democracies, the «Kefalonian Tetrapolis» (Sami, Krani, Palli and Pronnoi). Pronnoi occupied the south-east part of the island. According to the historian Polivios, Poros  must have been the port of the city of Pronnoi, situated on the hill above the village which is  nowadays known as Pastra.

The acropolis of Pronnoi gave the impression that Poros exists  since the classical period. Yet, the recent discovery and excavation of a great vaulted tomb  of the Mycenaean period, which was found at the location Broutzi of Tzanata, indicates that the area was populated much earlier, since prehistoric times. The tomb is the greatest and  the best preserved of those found on the island. Its diameter is 6,80 meters and it is built on  a rocky clearing of a hill. Inside the tomb were found many burials which are dated from  1400 to 1000 B.C. This tomb signals the existence of a mighty Mycenaean center, probably  that of the Homerian Ithaka.  Poros, following the history of the island, had many conquerors: Romans, Franks,  Venetians, Italians, French, Russians, Turks and finally the British, until 1864 when Kefalonia was united with Greece. In  1821 Napier, the British Governor of the island, afraid that the area would become unpopulated, brought settlers from Malta.  This model agricultural settlement that he intended to create never succeeded.