Today is the “agreed” date of the Battle of Marathon in 490 BCE , the first feature bout between Persia and Athens.
The city states of Athens and Eritria (link) had aided revolts (499 to 493 BCE) against Persian hegemony of the Greek speaking city states on the coast of Asia Minor, which Cyrus the Great had captured in 547 BCE. The revolt was crushed by Darius Iwho then vowed revenge on Athens.
There was no “Greece” at the time (nor would there be until the London Protocol in 1830 CE) but a collection of city states all around the eastern Mediterranean and Black Sea which shared the same culture, language and religion. A city-state was a sovereign state that consisted of a city and its dependent territories. Athens, Thebes, Sparta, are famous examples Greek city states (polis). Among other non-Greek city states were, Carthage, Rome and later, from 800CE, the Most Serene Republic of Venice.
Back to the match…
Darius set out to crush Athens by first capturing the Cyclades, and then Eritrea. From Evvia he sailed across the narrow South Evian gulf and landed at Marathon which had some flatlands surrounded by marshes (and a lot of fennel from which Marathon derives its name). Knowing the landscape and carefully choosing a spot to confront the invaders, outnumbered Greek speaking forces from Athens and tiny Plataea(link) KO’d the Persians and forced them back to their ships. This victory marked the end of the first Persian invasion of the Greek landmass. A rematch under Xerxes began 10 years later.