In 600 BC, Ionian Greeks from Phocaea founded the colony of Massalia (present-day Marseille), on the shores of the Mediterranean Sea. This makes it France's oldest city. At the same time, some Gallic Celtic tribes penetrated parts of Eastern and Northern France, gradually spreading through the rest of the country between the 5th and 3rd century BC. The concept of Gaul emerged during this period, corresponding to the territories of Celtic settlement ranging between the Rhine, the Atlantic Ocean, the Pyrenees and the Mediterranean. The borders of modern France roughly correspond to ancient Gaul, which was inhabited by Celtic ''Gauls''. Gaul was then a prosperous country, of which the southernmost part was heavily subject to Greek and Roman cultural and economic influences.