Xerxes first arrived in Greece following his father, Darius', first failed invasion. The year was 480 B.C.E. Known by the title Shahanshah, King of Kings, to the Persians, he launched the 2nd invasion that defined his reign, despite his many large building projects throughout the Persian Empire.
The 2nd invasion was championed by his cousin Mardonius, who hoped to rule as a satrap following their success, which many viewed as inevitable due to the vast size and force of the invading armies. Even though Herodotus exaggerated their numbers, the Persian forces were still of unprecedented size among ancient armies.
Despite early success throughout the Grecian countryside that culminated in the burning of Athens and a famous clash with Leonidas' 300 (among others) at Thermopylae, Xerxes' forces were ultimately repelled by Themistocles at the fleet battle of Salamis. This was accomplished through superior tactical use of the land to nullify the Persian numerical advantage, in this case by luring the Persians into the narrow straits and using the speed of their triremes to overwhelm the slower Persian ships.