The First Persian Invasion of Greece occurred in 490 BCE when the Persian Empire, led by King Darius I, sought to expand its territory. The invasion was primarily a response to the support that some Greek city-states, particularly Athens, had provided to the Ionian Revolt, where Greek cities in Asia Minor rebelled against Persian rule. The most notable battle during this invasion was the Battle of Marathon, where the Athenian army, despite being outnumbered, achieved a surprising victory over the Persians. This battle marked a significant moment in Greek history, showcasing the resilience of the Greek city-states against a powerful empire.