After the failure of the first invasion, Darius began raising a huge new army with which he intended to subjugate Greece completely. However, in 486 BCE, his Egyptian subjects revolted, and the revolt forced an indefinite postponement of any Greek expedition. Darius died while preparing to march on Egypt, and the throne of Persia passed to his son Xerxes I. Xerxes crushed the Egyptian revolt, and very quickly resumed the preparations for the invasion of Greece. Since this was to be a full-scale invasion, it needed longterm planning, stockpiling and conscription. Xerxes decided that the Hellespont would be bridged to allow his army to cross to Europe, and that a canal should be dug across the isthmus of Mount Athos (a Persian fleet had been destroyed in 492 BCE while rounding this coastline). These were both feats of exceptional ambition that would have been beyond the capabilities of any other contemporary state. However, the campaign was delayed by one year because of another revolt in Egypt and Babylonia.

The Persians had the sympathy of several Greek city-states, including Argos, which had pledged to defect when the Persians reached their borders. The Aleuadae family, who ruled Larissa in Thessaly, saw the invasion as an opportunity to extend their power. Thebes, though not explicitly 'Medising', was suspected of being willing to aid the Persians once the invasion force arrived.

In 481 BCE, after roughly four years of preparation, Xerxes began to muster the troops to invade Europe. Herodotus gives the names of 46 nations from which troops were drafted. The Persian army was gathered in Asia Minor in the summer and autumn of 481 BCE. The armies from the Eastern satrapies were gathered in Kritala, Cappadocia and were led by Xerxes to Sardis where they passed the winter. Early in spring, it moved to Abydos where it was joined with the armies of the western satrapies. Then the army that Xerxes had mustered marched towards Europe, crossing the Hellespont on two pontoon bridges.