Persia .
He had the captains of the Phoenician ships in his fleet, who lost their ships early in the battle, beheaded as an example to the others.
This is not known, but with 40 ships lost, perhaps 8,000.
It was a combined Greek force to which Sparta provided a contingent. They lost.The battle was a holding operation to force a sea battle on the nearby coast to remove the Persian fleet's threat to the southern cities and expose the Persian supply line. The Greeks lost the sea battle as well. The won a subsequent sea battle at Salamis ans a land battle at Plataia which decided the war in their favour.
The object was to destroy the Persian fleet. By blocking the pass it forced the Persian fleet to try to turn it by sea. The Greek fleet was waiting and engaged the Persian fleet. The Greek plan failed as they lost the sea battle.
Xerxes didn't cricify Leonidas. After he was killed in battle he had his head impaled on a pike. There is no record of any outcome of this act. Xerxes lost his war because of defeat in the sea battle of Salamis which had nothing to do with Leonidas.
He had the captains of the Phoenician ships in his fleet, who lost their ships early in the battle, beheaded as an example to the others.
They allowed themselves to be fooled into splitting their fleet, with the Egyptian third of it being sidelined from the battle. They allowed themselves to be dragged into entering the bay of Salamis, again splitting their fleet by going around both sides of Psyttalia Island and by moving in in two thin lines, exposed to mass flank attack in the narrow waters of the strait.
Xerxes I of Persia .
Having lost the sea battle of Salamis, they then lost the land battle of Plataea, leaving them with no power.
Persia invaded mainland Greece, defeated the combined Greek fleet at Artemesion, lost the sea battle of Salamis, lost the land battles of Plataia and Mycale, and withdrew back to Asia.
The Greek fleet lost the naval battle of Artemesion to the Persians. As the defence of the Thermopylai pass had been to force the naval battle, the force holding the pass was withdrawn as having no further purpost. A second successful sea battle was fought at Salamis.
The actual number of people who died in the Battle of Salamis is not recorded. However, more than 300 ships were lost, many of them with all hands.
Themistocles was the Athenian general that defeated the Persians at Salamis. He used military strategy and tricked the Persians into sailing into the straits where they lost needed mobility.
The Athenians did not fight at Thermopylai. A combined force of half a dozen other cities did. The Athenians manned their fleet at the parallel sea battle at Artemesion which was lost. Athens evacuated its populace to Peloponnesian cities and embarked its forces on its warships to fight in the Southern Greek fleet at the successful battle of Salamis, after which they returned to Athens which the Persians had evacuated.
The Athenians were not part of the force at Thermopylai. They were manning their navy, which was part of the naval force assembled at Artemesion in the nearby strait fighting the Persian fleet. After the sea battle was lost, the fleet retired to Salamis for another try. Meanwhile, they abandoned their city, sending their non-combatants to refuge in Peloponnesian cities.
army lacked the capacity to function as a unit and fought as individuals.
This is not known, but with 40 ships lost, perhaps 8,000.