Persian emperor Darius I 513 BC. went to Europe. He crossed the Bosporus and invaded Thrace. He then headed north across the Danube and attacked the Scythians (that is how the Greeks called the tribes north of the Danube, the Black and the Caspian Sea to the north and east). The cold, lack of food and water and guerrilla actions Scythians, forced Darius to retreat back to Asia.
After Darius failure in the north, Asia Minor Greeks (Ionians) had started preparing for the fight against Persian rule. Rebellion was known as the Ionian revolt.
499 BC. Ionian cities were uprising in Asia Minor led by Aristagoras. They were joined by some of Asia Minor Aeolian. In rebellious cities tyrannies was abolished and introduced democracy. The tyrants who were with the Persians had been exiled. Aristagoras requested help from Sparta, Athens and other Greek cities, but he did not got respond to some while others send too little of aid. The fighting of rebel cities and Persians lasted five years and ended by the insurgents defeat.The Miletus was burned, and Miletus were taken to Babylon.
The march of Darius– then the Darius I intended to realize his plan of conquest Greek. The first expedition was sent to 492 BC. when the army led by Mardonius crossed the Hellespont to the Thracian coast, but the navy was destroyed in a storm off Cape Athos. Mardonius was later attacked and he had to retreat back to Asia.
In early 490 BC. Darius had sent messengers to check that his Greek cities were loyal (he requested land and water). In the spring of 490 BC the navy was sent off the coast of the eastern Mediterranean, under the command of Datis and Artaphernes. Navy entered the Aegean Sea and went from island to island to Euboea, where they captured Eretria.
The Persians were then transferred to the nerby Attica coast, the Marathon field that was most suitable for the Persian cavalry. There they took by Hippia. The Athenians found out of it and headed towards Marathon, led by Miltiades. In September 490 BC. Athenians had clashed with the Persians at Marathon field, and they won. Many Persian had been killed, and the others retreated to the ship and headed south to the port Phalerum hoped to attack the undefended Athens. Athens military with rapid march came from Marathon to the Athens (marathon race) before the Persians. When they realized that, the Persians gave up the attack and returned to Asia.