Persians had conquered Ionia. Greeks revolted so Athens sent ships to help Greeks. Since the Athenians had gotten involved, the Persians had decided to get revenge which led to the Battle of Marathon.
Persians sent 25,000 across Aegean Sea to a plain called Marathon. There, 10,000 Athenians waited in a Phalanx. The Greeks charged and the Persians fled the battlefield.
Pheidippides ran 26 miles from Marathon to Athens to report Persian defeat and to not give up on Athens city without a fight.
10 years later, 7,000 Greeks and 300 Spartans blocked new leader Xerxes as he tried to march to Athens down the east coast of Greece through a narrow mountain where they were able to trap him.
A trader from the Greeks told the Persians about a secret path around the pass. All the Spartans were killed as they tried to help stop the Persians so that the rest could get to safety. In the end, Xerxes had won.
Xerxes sent his troops to trap the Greeks in a narrow channel near the Island of Salamis. The channel was too narrow for his troops too turn so 1/3 of his fleet had sank.