ancient helmet of a Greek hoplite

The Persian wars were a series of engagements between the massive Persian empire and the various city states of ancient Greece over the course of 40 years (499-449 BCE).  The tension between the Greeks and the empire of Persia is believed to have been a result of the violent uprising known as the Ionian Revolt in 499 BCE. At the time, the empire of Persia, and it’s ruler Darius the Great, had taken control of several civilizations in Asia minor, leaving tyrants to rule the various cities on behalf of the empire of Persia.
The city of Ionia would rebel against the Persians with the assistance of Athens. The Ionia revolt, although promising at first, would become something of a debacle. After one major offensive against the Persians, the rebels would be continuously put on the defensive for the rest of the military engagement. Persia would effectively crush the revolution and then set its sights across the Aegean to Athens. Darius the Great intended to punish the Greeks for their support of the failed revolution.
The battle of Marathon is often considered the military engagement that would define the first Persian invasion of Greece. The Persian army landed at the bay of Marathon with the intent of marching to Athens, some 26 miles away, and destroying the city as punishment for their defiance of the empire. Athens, under the guidance of the general Miltiades , would march their smaller army to Marathon and engage the Persian forces before they had a chance to attack Athens.
bronze shield

The Greeks used massive bronze shields to repel enemy soldiers

The battle of Marathon would be something of a strategic miracle for the Athenian army. Miltiades arranged his army in a narrow valley along the route to Athens with the intent of blocking the Persian advance. The narrow corridor would prevent the Persians from implementing their cavalry, which is often considered the source of their military dominance. The Persian infantry was now forced to march head on into a disciplined Athenian army with bronze shields and steeled determination.
The Greeks would see victory at Marathon. Their tactics would allow them to slaughter the approaching invaders and eventually force them back to their ships and across the Aegean sea. Miltiades sent a messenger to Athens to tell of the great victory. The man is said to have run the 26 miles, reached Athens and declared “Nike!”, the Greek word for ‘victory. He then promptly died in the city square. This story is the origin for the modern act of “running a marathon”.
Athens rejoiced in this great victory, convinced that the Persians were defeated permanently. However there was one man who knew that the war was really just beginning. A general at Marathon, this man would lay the foundation for the Greek defensive against the imminent second invasion. His name was Themistocles.
Themistocles quote

The Greek general, Themistocles

Themistocles was an Athenian politician who had risen to great political influence during the early years of Athenian democracy. He navigated the political landscape, destroying his opponents and continuously pushing his agenda of building the Athenian navy. Themistocles was convinced that the key to success against the next Persian invasion would be a dominant navy, and he would do anything to ensure that Athens was ready.
At this time, around 490 BCE, the son of Darius the Great was inheriting his fathers empire and preparing his army for a massive invasion of Greece. His name was Xerxes, and while Themistocles was desperately trying to bolster his navy; Xerxes was amassing the largest army that the ancient world had ever seen.
In 481 BCE Xerxes sent ambassadors across Greece demanding that all city-states submit to his empire. Sparta and Athens refused and, along with several smaller Greek cities, would form an alliance against their common enemy. The city-states of Greece, especially Athens and Sparta, had generally held a tradition of fighting and killing each other up until this point. The alliance therefore was a rather remarkable occurrence. Perhaps in the shadow of complete annihilation, the Greeks swallowed their pride and aligned themselves as one.
in 480 BCE, Xerxes marched his army across modern day Europe and then intended to march south towards Greece and Athens. The allies took up defensive positions in an attempt to block the advance of an army that outnumbered them 50 to 1. King Leonidas of Sparta, along with his 300 Spartans and some 7000 allied soldiers, took up position at the pass of Thermopylae. Meanwhile Themistocles and the newly built Athenian navy attempted to block the Persians by sea at the strait of Artemisium.
Leonidas at the Battle of Thermopylae

Leonidas at Thermopylae, by Jacques Louis David, 1814. This is a juxtaposition of various historical and legendary elements from the Battle of Thermopylae.

The allies used the same tactic that Miltiades had used at the battle of Marathon. By forcing the Persian army into a bottleneck, the smaller Greek army stood a chance at holding their ground. Similarly Themistocles hoped to outmaneuver the massive Persian ships by forcing them into the narrow strait of Artemisium. Both Leonidas and Themistocles battle bravely for two days. However Leonidas was killed along with most of the Spartans warrior and Xerxes was allowed to pass through Thermopylae.
map of thermopolyae

The battle of Thermopylae and the movements to Salamis

There was nothing stopping the massive Persian army and they marched onto Athens unchallenged. Themistocles had ordered the evacuation of Athens. Using the allied navy for support, Athens was evacuated and the citizens were transported to the island of Salamis, some thirty miles away. With nobody to defend the city, Xerxes raided Athens and set it to fire. It would appear that defeat was close at hand for the Greeks.
Themistocles would remain resolute. Using a clever form of subterfuge he sent an messenger to Xerxes explaining that the allied navy was harbored near Salamis and had fallen into chaos. Xerxes, hoping for a quick victory, ordered his navy to pursue the Greeks into the strait of Salamis. Instead of disorganized ships, the Persians were greeted by highly organized war vessels prepared for battle. The Greek navy broadsided the Persian fleet and utilized their maneuverability to outflank the cumbersome Persian ships. Within the narrow confines of the strait, the Persian armada fell into chaos.
The Greeks would see victory at Salamis and Xerxes himself would leave Greece not long after. Over the next several years the Greeks continued to engage the Persian army. However this time, the allies were on the offensive. Battling the Persian army across the Asia minor, the once invaders slowly retreated all the way back across the Aegean. The Greeks had staved off the second invasion, Greece would remain unconquered.