The battle of Artemisium (August 480 BC) was an inconclusive naval battle that was fought on the same three days as the battle of Thermopylae, and that ended when the Greek fleet retreated after learning of the Persian victory at Thermopylae (Greco-Persian Wars).
In 490 the Emperor Darius had sent an army across the Aegean to punish Eretria and Athens for their support of the Ionian Revolt. The Persians had been defeated at the battle of Marathon (490 BC), and Darius had died before he could launch a fresh invasion. His successor Xerxes decided to lead a massive invasion of Greece in person. He also decided not to risk another expedition across the Aegean, but instead to carry out a massive joint operation, leading a vast army and fleet along the coasts of Thrace and Thessaly and south to Athens.
Many Greek communities decided to accommodate the Persians, but a powerful coalition, led by Sparta and Athens, decided to resist. The Greek allies met at the Isthmus of Corinth and decided to make a stand at Tempe in Thessaly. It soon became clear that this position could easily be outflanked, and so they decided to defend the narrow pass of Thermopylae, at the southern border of Thessaly. The fleet was to defend the straits between Magnesia and the island of Euboea, with their initial base at the beach of Artemisium, near a shrine to Artemis.
According to Herodotus the Persians had 1,207 triremes at the start of their expedition - 300 from Phoenicia and Palestine, 200 from Egypt, 150 from Cyprus, 100 from Cilicia, 30 from Pamphylia , 50 from Lycia, 30 from the Dorian cities of Asia, 70 from Caria, 100 from Ionia, 17 from the Aegean islands, 60 from Aeolia and 100 from the Hellespont. Each ship carried a mix of Persian, Median and Sacian marines. Herodotus's vast figure of two million fighting men in the land army is normally dismissed as entirely unrealistic, but the size of the Persian fleet is perhaps more realistic.
The Persians suffered heavy losses before they ever clashed with the Greeks. As they sailed down the coast of Magnesia, they anchored between Casthanaea and Cape Sepias. The size of the Persian fleet acted against them, making it difficult for them to find any suitable harbours. According to Herodotus on this occasion they were moored eight-deep all along the beach. Overnight a powerful north-easterly storm hit the dangerously exposed Persian fleet. 400 warships and an unknown number of supply ships were lost during the three day storm. Another fifteen ships were lost when they sailed too far and inadvertently ran into the Greek fleet. If Herodotus's initial figure is to be believed, these loses brought the Persian fleet down to just under 800 ships (if all the lost warships were triremes), assuming none had been lost on the long journey from Asia Minor and along the coasts of Thrace and Thessaly. However they also received 120 reinforcements from Thrace, so may have had 920 ships.
According to Herodotus the Greeks had 271 triremes at the start of the battle. Athens provided 127 ships in her own contingent, with crews from Athens and Plataea. Corinth provided 40 ships, the Megarians 20, Chalcis provided 20 crews but the ships came from Athens. The Aeginetans provided 18 ships, the Sicyonians 12, the Lacedaemonians 10, the Epidaurians 8, the Eretrians 7, the Troezenians 5, the Styrians 2 and the Ceans 2 triremes and 2 penteconters. The Opuntian Locrians provided 7 penteconters. The fleet was commanded by the Spartan Eurybiades son of Euryclidas, after the other allies refused to follow an Athenian leader. The Athenian leader Themistocles, who had played a key part in building up the Athenian fleet, commanded the Athenian contingent and played a major part in ensuring that the fleet stood and fought.
After the storm the Persians continued south to Aphetae, at the southern tip of Magnesia. The Greek reaction suggests that they still had an apparently overwhelming numerical advantage, as both Eurybiades and Adeimantus, commander of the large Corinthian contingent, decided to withdraw. The Euboeans asked for time to evacuate their families from the island, but Eurybiades turned them down. The Euboeans then turned to the Athenian naval leader Themistocles, in one of the most controversial incidents of the battle (at least to modern eyes). Themistocles was offered thirty talents of silver to convince the fleet to stay. He bribed Eurybiades with five talents and Adeimantus with three talents, keeping the remaining twenty two talents himself. To modern eyes this looks like corruption, but it was clearly unremarkable behaviour at the time, and Herodotus says that both of the bribed leaders assumed the money had been sent from Athens for that purpose.
On the first day of the battle the Persians sent a detachment of 200 ships around Euboea to cut off the Greek line of retreat. The Greeks were informed of this move by a deserter, Scyllias of Scione, and attacked the temporarily weakened main Persian fleet (although if Herodotus's figures are right they were still outnumbered by two-to-one).
The Persians reacted to the Greek attack by forming into a ring and surrounding them. The Greeks responded by forming a circle and fighting with their sterns pointing towards the centre. The Greeks captured 30 ships during the first day of the battle. Their losses aren't recorded.
They intended to sail south that night to destroy the Persian detachment, but were kept in port by a massive storm that caught the Persians without shelter and destroyed most of the detachment.
On the second day 53 Athenian ships joined the fleet, bringing the total up to over 300. They also brought news of the Persian disaster, presumably having sailed through the same seas. The Persians were perhaps down to no more than 560-680 ships, but still outnumbered the Greeks.
There was some fighting on the second day, in which the Greeks defeated a Cilician contingent in the Persian fleet.
On the third day the Persians attacked at about noon. The Greeks fought in a half-moon formation. Both sides suffered heavy losses in this fighting. The Greeks just about held their own, but began to realise that they would probably have to retreat to avoid heavier losses. Meanwhile the Persians had outflanked the Greek position at Thermopylae, and during the day the last Greek rearguard was destroyed. The commanders of the fleet realised that they needed to retreat from Artemisium, and pulled back to the straits of Salamis, where they hoped the narrow waters would allow them to take advantage of their heavier ships. While they were moving south Themistocles stopped at every source of fresh water and had a message carved into the rocks asking the Ionian Greeks to desert the Persians.
A number of famous Greeks fought at Artemisium. Amongst them was the Aeschylus, the first great Athenian writer of tragic plays