The Battle of Marathon took place in 490 BC, during the first Persian invasion of Greece. It was fought between the citizens of Athens, aided by Plataea, and a Persian force commanded by Datis and Artaphernes. It was the culmination of the first attempt by Persia, under King Darius I, to subjugate Greece.
Herodotus, the great historian of the Persian Wars, makes it clear in his Histories that Xerxes was looking to revenge himself primarily against Athens for the humiliating defeat [at Marathon] that city had inflicted upon his father:
"I will bridge the Hellespont and march an army through Europe into Greece, and punish the Athenians for the outrage they committed upon my father and upon us. As you saw, Darius himself was making his preparations for war against these men; but death prevented him from carrying out his purpose. I therefore, on his behalf, and for the benefit of all my subjects, will not rest until I have taken Athens and burnt it to the ground, in revenge for the injury which the Athenians without provocation once did to me and my father."
Herodotus, the great historian of the Perisan Wars, makes it clear in his Histories that Xerxes was looking to revenge himself primarily against Athens for the humiliating defeat that city had inflicted upon his father:
"I will bridge the Hellespont and march an army through Europe into Greece, and punish the Athenians for the outrage they committed upon my father and upon us. As you saw, Darius himself was making his preparations for war against these men; but death prevented him from carrying out his purpose. I therefore, on his behalf, and for the benefit of all my subjects, will not rest until I have taken Athens and burnt it to the ground, in revenge for the injury which the Athenians without provocation once did to me and my father.
While there were many other battles to come, Marathon was the most crucial and pivotal for several reasons. Firstly, it reinvigorated the Greek resistance and demoralised the Persian troops. Secondly, it was the first battle where the Greeks had resisted the Persians and been victorious; moreover, they had done so with inferior numbers. Thirdly, it cost the Persians a good portion of their attack force, blunting the following battles that would come, and that would fail.
Legend has it that Pheilippides, an Athenian courier, ran from the battlefield to Athens, announced the victory, and collapsed in death. He was in fact the one who was sent to alert the Spartans earlier in the month and covered the 150 miles in 2 days, but the run to Athens after the battle probably did not happen. This, however, is the basis of the modern marathon race, supposedly the distance he ran to announce the battle's outcome.
The Persians did not give up, but hurried away as fast as their oars could drive them. Not a moment's rest was there for the weary Greeks, for the vessels were pointed toward Athens. The soldiers marched off at full speed; and when the Persians arrived and saw them encamped on a little river close to the city, they went back to their own country.
The Athenians suddenly advanced at a run towards the enemy who were about a mile away...
The struggle was long and drawn out. In the centre the advantage was with the Persians; but however the Athenians and the Plateans on the wings were both victorious. They drew both wings together into a single unit and chased the Persians in the centre, cutting them down until they came to the sea.
The Athenians secured seven ships but the rest escaped and sailed out to sea.
Meanwhile the Athenians were drawn up on a piece of ground sacred to Heracles where they were joined by the Plateans (allies of the Athenians from the north) who came to support them with every available man (probably about 1000).
The Persians left their camp, marched south along the shore, crossed the bed of the Charadra river and formed a line of battle opposite the Greek position. For several days both armies faced each other without moving. The Greeks were probably waiting for the arrival of the Spartans whilst the Persians may have been hoping to keep the Greek army immobile tactically and meanwhile move a maritime force independently against an unguarded Athens.
A Persian fleet sails along the southern coast of Anatolia. According to Herodotus, it numbers 600 ships...
From Ionia this armada sets a course straight across the Aegean, pausing only at Naxos and other islands to take hostages and press recruits into the army. The destination is Marathon, a plain to the north of Athens on which the cavalry will have room to manoeuvre. The army lands on the island of Euboea, conquers the small city of Eretria, makes the short crossing to the mainland at Marathon, and waits.
...[in] 491 B.C., Darius decided to try to take over Greece without fighting. He sent heralds - ambassadors - to each city state in Greece, asking for earth and water. This was a symbol for submission - giving over your land and sea to Persia.
At Sparta, King Kleomenes pushed the heralds into a well, saying 'get your earth and water there.'
At Athens, general Miltiades persuaded the Athenian citizens to vote for executing the heralds. Like the Spartans, they pushed them into a hole on the ground - a chasm called the barathron. Eretria also refused earth and water, as did a few other cities.
Darius then became intent on subjugating all the Greeks, especially the Athenians, and punishing them for their part in the Asian revolt.
In 492 BC he dispatched an army under his son-in-law, Mardonius. This army again reduced Thrace and compelled Alexander I of Macedon to submit to Persia. However, in attempting to advance further into Greece much of the fleet was wrecked in a storm and Mardonius was forced to retreat back to Asia.
As overlords of Ionia, the Persian kings installed and supported tyrants in its city-states. By 499 B.C. the Ionians were tired of Persian-backed tyranny and suffered from internal unrest. They rebelled, sending representatives to mainland Greece to ask for help in their revolt against Persia...The men of the Athenian assembly...voted to join the city-state of Eretria on the neighboring island Euboea and send military aid to the Ionians. The combined Athenian-Eretrian force actually got as far as Sardis, Croesus' old capital, now the headquarters of a Persian provincial governor. After burning Sardis to the ground, however, the Athenians and Eretrians returned home when a Persian counterattack caused the Ionian allies to lose their coordination. Subsequent campaigns by the Persian king's commanders crushed the Ionian rebels by 494 B.C.