Then he began to fall back.
Thick weather favoured him, and Ney assembled a large force near Leiria, as if to advance against the British position.

Two other corps left Santarem, on the night of the fifth, and retired to Thomar.

The rest of the army moved by other routes.
For four days Wellington, although discovering that a retreat was in progress, was unable to ascertain by which line Massena was really retiring.

As soon as this point was cleared up, he ordered Beresford to concentrate near Abrantes; while he himself followed the line the main body of the French army seemed to be taking.

It was soon found that they were concentrating at Pombal, with the apparent intention of crossing the Mondego at Coimbra; whereby they would have obtained a fresh and formidable position behind the Mondego, with the rich and untouched country between that river and the Douro, upon which they could have subsisted for a long time.
Therefore, calling back the troops that were already on the march to relieve Badajos, which had not yet surrendered, he advanced with all speed upon Pombal, his object being to force the French to take the line of retreat through Miranda for the frontier, and so to prevent him from crossing the Mondego.
Ney commanded the rear guard, and carried out the operation with the same mixture of vigour, valour, and prudence with which he, afterwards, performed the same duty to the French army on its retreat from Moscow.