The King of Persia, Xerxes, wanted to expand his empire and so assembled a great army and naval force. In September 480 BCE having defeated Macedonia, Xerxes moved on to conquer Greece.
By the middle of September the Persians had forced the Greeks to abandon Athens. A small Greek force remained behind to try to defend the city. The Greek navy had withdrawn to the island of Salamis.
On 17th September Athens fell and the Greek garrison was defeated. Xerxes decided to attack the Greek ships and Athenians that had retreated to Salamis. Xerxes was confident that his 700 ships would easily defeat the Greek fleet of 300 ships and sailed for Salamis.
The Greek commander Themistocles persuaded the Greek naval captains to stay where they were rather than to flee to open waters. At the same time he sent a spy to tell the Persians where the Greek ships were and advise them that if they were quick they could block the Greeks in the straits between Salamis and Attica. The Persians were convinced and on the 20th September sailed to Salamis.
As the Persians sailed into the narrow strait between Salamis and Attica the Greeks were able to ram the ships and drive them, one by one, towards the shores of Attica. By the end of the day the Persians had been defeated.