During the second Persian invasion of Greece, Athens was led by Themistocles. He had fought at the Battle of Marathon ten years earlier, and was wary of the threat posed by Persia, even before they returned under Xerxes. He went to see the Oracle at Delphi, and asked her how he could keep his city safe. She cryptically advised him: “Trust in your wooden walls.” Themistocles interpreted this as meaning that he should massively build up Athens’ navy. During the Second Greco-Persian War, all could see the wisdom in his decision.
At the same time as the Battle of Thermopylae, there was also an important naval engagement called the Battle of Artemisium. Led by Themistocles and the Spartan Eurybiades, this battle took a very similar form to the simultaneous land battle. The allied Greek fleet made its stand at the Straits of Artemisium to prevent the much larger Persian navy from reaching the rest of Greece.
The Greeks assembled a fleet of 271 ships, which contained 4,065 marines and were propelled by 46,070 rowers. The Persian armada, by comparison, was made up of 1,207 ships, 36,210 marines, and 205,190 rowers. As with on land, the Greeks were heavily outnumbered, but held a tactically advantageous position.
Herodotus noted that the Persian ships were more maneuverable. Additionally, most of the Greek fleet was newly built, and the sailors were therefore less experienced. The Greek fleet was able to counteract the greater maneuverability of their enemy by drawing their ships into a circular or crescent formation, with the armored prows facing outward and the more vulnerable sterns and flanks protected by their allies. They were able to suddenly strike outwards after being given the signal, catching the Persians off guard.
The day progressed with the Greek fleet doing better than the Persians would have expected. They were able to take out 30 Persian vessels before a storm struck during the night. The Persian fleet had already weathered a storm before the battle began, and now elected to repair their fleet rather than launch another attack on the Greek position. In the meantime, the Greeks received a reinforcement of 53 ships from Athens. They intercepted and destroyed a small patrol from the Persian fleet, but no major engagements occurred on the second day of the battle.
On the third day the Persians assembled their fleet to attack again. The Greeks blocked the strait and stood their ground. The Persian fleet sent their flanks forward in a crescent formation to flank the Greeks. The two armadas met and fought a long and hard battle throughout the day. The Greeks were greatly outnumbered, but made a good showing. The Athenians were the best naval fighters on the Greek side, taking down many enemy vessels. The greatest sailors on the Persian side were the Egyptians, who were more heavily armed and armored than their allies and were able to sink five Greek ships, according to Herodotus. The two sides lost roughly equal numbers during the day, but the Greek fleet could not take these losses as well as the Persians.
When the fleets broke off for the night, the Greeks saw that they would not be able to hold the pass for another day. Additionally, they received word that the army at Thermopylae had fallen. Knowing that there was now no more strategic value to holding Artemisium, coupled with their reduced ability to do so, the Greek fleet left the strait. The Persian fleet then moved forward and sacked the city of Histiaea and the surrounding area.
With the path opened both on land and sea, the Persians were free to invade the rest of Greece. The cities of Thespiae and Plataea quickly fell. The Persian army soon reached Athens, which had only just been evacuated before they reached the city. All that remained was a small garrison on the Acropolis, which was swiftly defeated. Wanting revenge for their defeat at Marathon ten years earlier, they burned the city to the ground.
Xerxes had spent more time on the frontier of his empire than he wished, and was worried about the state of his capital after spending so much time away. His priority now was to end the conquest of Greece as quickly as possible. The remaining free Greek cities were heavily fortified, so he prioritized gaining naval supremacy so he could outflank the Greek armies. Knowing that the course of the war would likely hinge on the outcome of naval combat, the Greek cities gathered their fleet at the narrow strait of Salamis. Here, they hoped to lure the Persian fleet into battle.
One of the Persian commanders saw through the Greek ruse. Artemisia, queen of the Persian Satrap of Caria, advised Xerxes to not attack the Greek fleet, as the Persians would lose their numerical advantage in the enclosed channel. She was ignored, though, and the Persian fleet soon began to prepare their strike.
The Persian fleet took position at both ends of the strait to box the Greeks inside. This worked to the Greeks’ advantage. The Persian fleet was stronger in open water, but the Greek fleet was better suited for fighting within narrow confines, as the Battle of Artemisium demonstrated. The Greek fleet launched in multiple directions at once, making it look like they were in disarray. The Persians took the bait and attacked. Their formations soon fell apart in the choppy waters and the Greek ships easily took apart the scattered and disorganized Persian fleet.
Artemisia was able to escape from the Greek ambush, and returned to Xerxes. The Emperor ordered his navy to retreat and sent his children back to Persia on Artemisia’s ship. Lamenting the loss of his fleet, he observed, “my men have become women and my women have become men.”
After observing his navy’s defeat, Xerxes spent the next several days considering his next move. He soon decided that he needed to return to Persia to manage the empire, and left his general Mardonius in Greece with about 80,000 men to continue the campaign. Mardonius attempted to find new allies in Greece. He found some success, convincing the city of Thebes to join his army. However, the war would soon be decided at Plataea.
Links
The Battle of Salamis, at the World History Encyclopedia
muscularhistory.com 
