In 540 B.C., at Alalia the Phocaean Greeks of Massillia defeated an Etruscan-Carthaginian alliance in the epic naval action of the Battle of Sardinia Sea, opening the Gibraltar Strait and enabling Greek colonization in the Western Mediterranean.
Greeks Win The Battle of Sardinia SeaThe Phoenicians had planted trading posts in Africa, Sicily, Sardinia and Iberia during 1100-900 BC while creating their trading monopoly. They had a relatively free hand during that period as other civilizations were suffering from a "Dark Age" during that period. The Etruscans emerged as a local power during 800 - 700 BC, spreading their trade to Corsica, Sardinia and Iberia and creating a powerful navy to guard their interests. The Phoenicians and Etruscans became trading partners and rivals, exchanging goods and opportunistic raids with each other. The situation changed with the arrival of the Greeks in Western Mediterranean in 750 BC.
The Greek colonization started with the planting of Cumae in Italy by 750 BC and Naxos in Sicily by 735 BC. Within the next 100 years, several Greek cities had planted colonies along the coast of southern Italy and most of Sicily, creating a position to control trade routes around these areas and dominating the Strait of Messina. Etruscans clashed with the Greeks, but were unable to stop the process. Although the colonization process was not done according to any master plan, with several Greek cities acting simultaneously, it probably seemed to the Phoenicians and Etruscans that a flood of Greeks were drowning the Tyrrhenian seacoast.
According to Herodotus, the Greeks only had sixty pentekonters (ships with 48 oars and 2 rudders for steering) but managed to drive off an allied fleet twice as large. By opening the Gibraltar Strait, the Phocaean Greeks opened up the the Western Mediterranean for colonization. And gained access to the ultimate prize, the hidden mysteries buried on an island West of the Azores - Atlantis which had been abandoned over nine thousand years before.