During the Tertiary Period, the Eocene period that is 50 million years ago, Peloponnese was under the surface of Tethys , an oceanic sea which extended from the Atlantic Ocean to the Pacific Ocean, parallel to the Equator. 25 million years ago, the lithospheric plates of the earth started moving. A uniform land was formed and is, today, occupied by mainland and insular Greece. It was then that Mt Parnon emerged from sea waters. But 12 million years ago, it sank and remained in this state till about 1 million years ago. Due to major geologic and climatic variations, Greece was covered with glaciers and sea level was reduced by 200 m. But once again, the massif of Parnon was covered by the sea and remained underneath till 12,000 years ago, when it got its today form.