First Persian invasion of Greece
The first Persian invasion of Greece took place from 492 BC to 490 BC, as part of the Greco-Persian Wars. It ended with a decisive Athenian-led victory over the Achaemenid Empire during the Battle of Marathon. Consisting of two distinct campaigns, the invasion of the independent Greek city-states was ordered by the Persian king Darius the Great, who sought to punish Athens and Eretria after they had supported the earlier Ionian Revolt. Additionally, Darius also saw the subjugation of Greece as an opportunity to expand into Southeast Europe and thereby ensure the security of the Achaemenid Empire's western frontier.
The first campaign, in 492 BC, was led by the Persian commander Mardonius, who re-subjugated Thrace and forced Macedon to become a fully subordinate client kingdom within the Achaemenid Empire; it had been a Persian vassal as early as the late 6th century BC—probably in 512 BC. However, further progress was prevented when Mardonius' fleet was wrecked in a storm off the coast of Mount Athos. The following year, having demonstrated his intentions, Darius sent envoys to all parts of Greece, demanding their submission. He received it from almost all of them, but not from Athens and Sparta, both of which executed the envoys sent to them. With Athens still defiant, and Sparta now effectively at war with the Persians, Darius ordered a further military campaign for the following year.
The second Persian campaign, in 490 BC, was led by the Persian commanders Datis and Artaphernes. The expedition headed first to Naxos, which was captured and burned, and then leapfrogged between the rest of the Cycladic Islands, annexing each of them into the Achaemenid Empire. Reaching Greece, they landed at Eretria, which they besieged, and after a brief time, captured. The Eretrians were enslaved and their city was burned. Finally, the expedition headed to Attica, landing at Marathon, en route to Athens. There, they were met by a smaller Athenian army, which nevertheless proceeded to secure for itself a remarkable victory.
This defeat prevented the successful conclusion of the campaign, and the Persian expedition returned to West Asia, though they had fulfilled most of their aims, successfully punishing Naxos and Eretria and bringing much of the Aegean under Persian rule, as well as fully integrating Macedon. The unfinished business from this campaign led Darius to prepare for a much larger invasion of Greece, aimed at firmly subjugating it and punishing Athens and Sparta. However, internal strife within the Achaemenid Empire delayed this expedition, and Darius then died of old age. It was thus left to his son Xerxes I to lead the second Persian invasion of Greece, which began in 480 BC.
Background
The first Persian invasion of Greece had its immediate roots in the Ionian Revolt, the earliest phase of the Greco-Persian Wars. However, it was also the result of the longer-term interaction between the Greeks and Persians. In 500 BC the Persian Empire was still relatively young and highly expansionist, but prone to revolts amongst its subject peoples. Moreover, the Persian king Darius was a usurper, and had spent considerable time extinguishing revolts against his rule. Even before the Ionian Revolt, Darius had begun to expand the Empire into Europe, subjugating Thrace, expanding past the Danube river, conquering Paeonia, and forcing Macedon to become a client kingdom to Persia; though the latter retaining an amount of autonomy up to 492 BC. Attempts at further expansion into the politically fractious world of Ancient Greece may have been inevitable. However, the Ionian Revolt had directly threatened the integrity of the Persian empire, and the states of mainland Greece remained a potential menace to its future stability. Darius thus resolved to subjugate and pacify Greece and the Aegean, and to punish those involved in the Ionian Revolt.The Ionian revolt had begun with an unsuccessful expedition against Naxos, a joint venture between the Persian satrap Artaphernes and the Miletus tyrant Aristagoras. In the aftermath, Artaphernes decided to remove Aristagoras from power, but before he could do so, Aristagoras abdicated, and declared Miletus a democracy. The other Ionian cities, ripe for rebellion, followed suit, ejecting their Persian-appointed tyrants, and declaring themselves democracies. Aristagoras then appealed to the states of Mainland Greece for support, but only Athens and Eretria offered to send troops.
File:Darius detail on the Darius vase.jpg|thumb|left|Drawing of Darius the Great and its inscription on the "Darius Vase"
The involvement of Athens in the Ionian Revolt arose from a complex set of circumstances, beginning with the establishment of the Athenian Democracy in the late 6th century BC.
In 510 BC, with the aid of Cleomenes I, King of Sparta, the Athenian people had expelled Hippias, the tyrant ruler of Athens. With Hippias's father Peisistratus, the family had ruled for 36 out of the previous 50 years and fully intended to continue Hippias's rule. Hippias fled to Sardis to the court of the Persian satrap, Artaphernes, and promised control of Athens to the Persians if they were to help restore him. In the meantime, Cleomenes helped install a pro-Spartan tyranny under Isagoras in Athens, in opposition to Cleisthenes, the leader of the traditionally powerful Alcmaeonidae family, who considered themselves the natural heirs to the rule of Athens. In a daring response, Cleisthenes proposed to the Athenian people that he would establish a 'democracy' in Athens, much to the horror of the rest of the aristocracy. Cleisthenes's reasons for suggesting such a radical course of action, which would remove much of his own family's power, are unclear; perhaps he perceived that days of aristocratic rule were coming to an end anyway; certainly he wished to prevent Athens becoming a puppet of Sparta by whatever means necessary. However, as a result of this proposal, Cleisthenes and his family were exiled from Athens, in addition to other dissenting elements, by Isagoras. Having been promised democracy however, the Athenian people seized the moment and revolted, expelling Cleomenes and Isagoras. Cleisthenes was thus restored to Athens, and at breakneck speed began to establish democratic government. The establishment of democracy revolutionised Athens, which henceforth became one of the leading cities in Greece. The new-found freedom and self-governance of the Athenians meant that they were thereafter exceptionally hostile to the return of the tyranny of Hippias, or any form of outside subjugation; by Sparta, Persia or anyone else.
Cleomenes, unsurprisingly, was not pleased with events, and marched on Athens with the Spartan army. Cleomenes's attempts to restore Isagoras to Athens ended in a debacle, but fearing the worst, the Athenians had by this point already sent an embassy to Artaphernes in Sardis, to request aid from the Persian Empire. Artaphernes requested that the Athenians give him an 'earth and water', a traditional token of submission, which the Athenian ambassadors acquiesced to. However, they were severely censured for this when they returned to Athens. At some point later Cleomenes instigated a plot to restore Hippias to the rule of Athens. This failed and Hippias again fled to Sardis and tried to persuade the Persians to subjugate Athens. The Athenians dispatched ambassadors to Artaphernes to dissuade him from taking action, but Artaphernes merely instructed the Athenians to take Hippias back as tyrant. Needless to say, the Athenians balked at this, and resolved instead to be openly at war with Persia. Having thus become the enemy of Persia, Athens was already in a position to support the Ionian cities when they began their revolt. The fact that the Ionian democracies were inspired by the example of Athens no doubt further persuaded the Athenians to support the Ionian Revolt; especially since the cities of Ionia were originally Athenian colonies.
File:Ionian Revolt Sardis campaign.jpg|thumb|The Athenians led a campaign against the Achaemenid capital of Sardis in Asia Minor in 498 BC, during the Ionian revolt.
The city of Eretria also sent assistance to the Ionians for reasons that are not completely clear. Possibly commercial reasons were a factor; Eretria was a mercantile city, whose trade was threatened by Persian dominance of the Aegean. Herodotus suggests that the Eretrians supported the revolt in order to repay the support the Milesians had given Eretria in a past war against Chalcis.
The Athenians and Eretrians sent a task force of 25 triremes to Asia Minor. Whilst there, the Greek army surprised and outmaneuvered Artaphernes, marching to Sardis and there burning the lower city. However, this was as much as the Greeks achieved, and they were then pursued back to the coast by Persian horsemen, losing many men in the process. Despite the fact their actions were ultimately fruitless, the Eretrians and in particular the Athenians had earned Darius's lasting enmity, and he vowed to punish both cities. The Persian naval victory at the Battle of Lade all but ended the Ionian Revolt, and by 493 BC, the last hold-outs were vanquished by the Persian fleet. The revolt was used as an opportunity by Darius to extend the empire's border to the islands of the East Aegean and the Propontis, which had not been part of the Persian dominions before. The completion of the pacification of Ionia allowed the Persians to begin planning their next moves; to extinguish the threat to the empire from Greece, and to punish Athens and Eretria.
492 BC: Mardonius' campaign
In the spring of 492 BC an expeditionary force, to be commanded by Darius's son-in-law Mardonius, was assembled, consisting of a fleet and a land army. Whilst the ultimate aim was to punish Athens and Eretria, the expedition also aimed to subdue as many of the Greek cities as possible. Departing from Cilicia, Mardonius sent the army to march to the Hellespont, whilst he travelled with the fleet. He sailed round the coast of Asia Minor to Ionia, where he spent a short time abolishing the tyrannies that ruled the cities of Ionia. Ironically, since the establishment of democracies had been a key factor in the Ionian Revolt, he replaced the tyrannies with democracies. Mardonius' establishment of democracy here can be seen as a bid to pacify Ionia, allowing his flank to be protected as he advanced towards the Hellespont and then onto Athens and Eretria.Thence the fleet continued on to the Hellespont, and when all was ready, shipped the land forces across to Europe. The army then marched through Thrace, re-subjugating it, since these lands had already been added to the Persian Empire in 512 BC, during Darius's campaign against the Scythians. Upon reaching Macedon, the Persians forced it to become a fully subordinate part of the Persian Empire; they had been vassals of the Persians since the late 6th century BC, but retained their general autonomy.
Meanwhile, the fleet crossed to Thasos, resulting in the Thasians submitting to the Persians. The fleet then rounded the coastline as far as Acanthus in Chalcidice, before attempting to round the headland of Mount Athos. However, they were caught in a violent storm, which drove them against the coastline of Athos, wrecking 300 ships, with the loss of 20,000 men.
Then, whilst the army was camped in Macedon, the Brygians, a local Thracian tribe, launched a night raid against the Persian camp, killing many of the Persians, and wounding Mardonius. Despite his injury, Mardonius made sure that the Brygians were defeated and subjugated, before leading his army back to the Hellespont; the remnants of the navy also retreated to Asia. Although this campaign ended ingloriously, the land approaches to Greece had been secured, and the Greeks had no doubt been made aware of Darius's intentions for them.