Battle of Artemisium happened on 10-09-08.

The Persians won the Battle of Artemisium, though not in a crushing manner.

They needed to destroy the Persian fleet, which threatened the southern Greek cities and so forced them to stay at home defending their cities and so were unable to unite. So they set up a blocking force at the pass of Thermopylae to force the Persians to try to turn the position by sea, with their own fleet waiting to pounce in the narrow waters at Artemesion.

Unfortunately for them, their fleet was defeated, so they withdrew the blocking force as no longer of use. The Spartan and hespian contingents remained to protect the withdrawal and were slaughtered.

The Battle of Thermopylae took place over three days during the second Persian invasion of Greece. It took place simultaneously with the naval Battle of Artemisium, in August or September 480 BC, at the pass of Thermoplaye ('The Hot Gates'). It was fought between an alliance of Greek city-states, led by Sparta, and the Persian empire of Xerxes I. The Persian invasion was a delayed response to the defeat of the first Persian invasion of Greece, which had been ended by the Athenian victory at the Battle of Marathon. Xerxes had amassed a huge army and navy, and set out to conquer all of Greece. The Athenian general Themistocles had proposed that the Allied Greeks block the advance of the Persian army at the pass of Thermo, and simultaneously block the Persian navy at the Straits of Artemisium.

An Allied force of approximately 7,000 men thus marched north to block the pass in the summer of 480 BC. The Persian army, alleged by the ancient sources to have numbered in the millions, arrived at the pass in late August or early September. Vastly outnumbered, the Greeks held up the Persians for seven days in total (including three of battle), before the rear-guard was annihilated in one of history's most famous last stands. During two full days of battle, the small force led by King Leonidas of Sparta blocked the only road by which the massive Persian army could pass. After the second day of battle, a local resident named Ephialtes betrayed the Greeks by revealing a small path that led behind the Greek lines. Aware that they were being outflanked, Leonidas dismissed the bulk of the Greek army, and remained to guard the rear with 300 Spartans, 700 Thespians, 400 Thebans and perhaps a few hundred others, the vast majority of whom were killed.

After this engagement, the Allied navy at Artemisium received news of the defeat at Thermopylae. Since their strategy required both Thermopylae and Artemisium to be held, and given their losses, the Allied navy decided to withdraw to Salamis. The Persians overran Boeotia and then captured the now-evacuated Athens. However, seeking a decisive victory over the Persian fleet, the Allied Greek fleet attacked and defeated the invaders at the Battle of Salamis in late 480 BC. Fearing to be trapped in Europe, Xerxes withdrew with much of his army to Asia, leaving Mardonius to complete the conquest of Greece. The following year, however, saw an Allied army decisively defeat the Persians at the Battle of Plataea, thereby ending the Persian invasion

To block the pass to provoke a sea battle. The Persian fleet was a threat to the Greek cities which kept their armies defensively at home. If the Persian fleet was destroyed, the Greek city armies could come out and unite to face the Persian army. Also the Persian supply fleet carrying food and forage for the army from Asia Minor would be exposed and the army could not be sustained in such a poor countryside as Greece.

The Persian strategy was to threaten the cities with its navy and so stop the Greek city land forces uniting. They could then pick the cities off one at a time - easy pickings. Athens had to be abandoned as a starter.

Unfortunately for the Greeks their attempt on the sea battle of Artemesion in the strait next to Thermopylai was lost, so the Thermopylai force now had no task and was withdrawn. The Greeks tried again at Salamis near Athens and won. The Persians could not feed themselves without the supply fleet from Asia Minor, and had to send half their army home. This made it easier for the Greek armies, which could now combine with the amphibious threat to their cities gone, to defeat the Persian army at Plataia the following spring.