His fleet was ordered to sail straight for the Hellespont, and to guard the bridges until he reached them with his army.

He himself retreated hastily along the same road by which he had advanced, his whole army accompanying him as far as Thessaly, where Marnonius was left with 260,000 picked men, to prevent pursuit, and to renew the attempt against Greece in the ensuing year.
Xerxes pressed on to the Hellespont, losing vast numbers of his troops by famine and sickness on the way, and finally returned into Asia, not by his magnificent bridge, which a storm had destroyed, but on board a vessel, which, according to some, narrowly escaped shipwreck during the passage.

Even in Asia disaster pursued him.

Between Abydos and Sardis his army suffered almost as much from over-indulgence as it had previously suffered from want; and of the mighty host which had gone forth from the Lydian capital in the spring not very many thousands can have re-entered it in the autumn.
Still, however, there was a possibility that the success which his own arms had failed to achieve might reward the exertions of his lieutenants.

Mardonius had expressed himself confident that with 300,000 picked soldiers he could overpower all resistance, and make Greece a satrapy of Persia.