Persians took over the Greek city-states in Ionia (Asia.)
Battle of Marathon
Ionians revolted against Persians, with help from other city-states like Athens.
In 499 BCE, the Persians defeated the Ionians and decided to punish the other city-states on mainland Greece for helping Ionians.
Battle of Salamis
You'll be safe behind this wooden wall.
Darius sent a Persian fleet across the Aegean Sea to the city of Marathon.
Persians decided to attack Athens directly because they wouldn't move; they ended up loosing.
Oracle at Dephi said Greeks would be safe behind a "wooden wall", but Athenian General Themistocles believed "wooden wall" meant fleet of the ships and that they needed to challenge the Persians at sea.