Upon assuming the throne, the Commander and Chief of his army, Mardonius, pressured to reignite the campaign ,Darius died too early to complete, against Greece. But before Xerxes could resume the campaign he had other matters to attend to such as the insurrection of Babylon and the revolts against Persian rule in Egypt, and Xerxes expended considerable time throughout the year 485 BCE in quelling these and restoring order.
Once relative peace was established in his empire, he was free to turn his attention back to Greece and the punishment of the Athenians, Naxians, and Eretrians for their interference in the Ionian Revolt, the burning of Sardis, and their victory over the Persians at Marathon.
Two pontoon bridges later known as Xerxes' Pontoon Bridges were built across the Hellespont. Soldiers of many nationalities served in the armies of Xerxes from all over his multi-ethnic massive Eurasian-sized empire and beyond, including the Assyrians, Phoenicians, Babylonians, Egyptians, Jews, Macedonians, European Thracians, Paeonians, Achaean Greeks, Ionians, Aegean islanders, Aeolians, Greeks from Pontus, Colchians, and many more.
According to the Greek historian Herodotus, Xerxes's first attempt to bridge the Hellespont ended in failure when a storm destroyed the flax and papyrus cables of the bridges. In retaliation, Xerxes ordered the Hellespont (the strait itself) whipped three hundred times, and had fetters thrown into the water. Xerxes's second attempt to bridge the Hellespont was successful. The Carthaginian invasion of Sicily deprived Greece of the support of the powerful monarchs of Syracuse and Agrigentum - ancient sources assume Xerxes was responsible. Many smaller Greek states, moreover, took the side of the Persians, especially Thessaly, Thebes and Argos. Xerxes was victorious during the initial battles.
Xerxes set out in the spring of 480 BC from Sardis with a fleet and army which Herodotus estimated was roughly one million strong along with 10,000 elite warriors named the Persian Immortals. More recent estimates place the Persian force at around 60,000 combatants.
Xerxes also conquered Thermopylae and soon after, Athens was captured. Most of the Athenians had abandoned the city and fled to the island of Salamis before Xerxes arrived. A small group attempted to defend the Athenian Acropolis, but they were defeated. Xerxes burnt the city; leaving an archaeologically attested destruction layer, known as the Perserschutt. The Persians thus gained control of all of mainland Greece to the north of the Isthmus of Corinth.
After the military blunders in Greece, Xerxes returned to Persia and oversaw the completion of the many construction projects left unfinished by his father at Susa and Persepolis. He oversaw the building of the Gate of All Nations and the Hall of a Hundred Columns at Persepolis, which are the largest and most imposing structures of the palace. He oversaw the completion of the Apadana, the Palace of Darius and the Treasury, all started by Darius, as well as having his own palace built which was twice the size of his father's. His taste in architecture was similar to that of Darius, though on an even more gigantic scale. He also maintained the Royal Road built by his father and completed the Susa Gate and built a palace at Susa.
In 465 BC, Xerxes was murdered by Artabanus, the commander of the royal bodyguard and the most powerful official in the Persian court