The French, pressing hard upon their heels and confident that the end was near, were brought up sharply before those stupendous, unsuspected, impregnable fortifications.
After spending best part of a month in vain reconnoitering, Massena took up his quarters at Santarem, and thence the country was scoured for what scraps of victuals had been left to relieve the dire straits of the famished host of France.

How the great marshal contrived to hold out so long in Santarem against the onslaught of famine and concomitant disease remains something of a mystery.

An appeal to the Emperor for succour eventually brought Drouet with provisions, but these were no more than would keep his men alive on a retreat into Spain, and that retreat he commenced early in the following March, by when no less than ten thousand of his army had fallen sick.
Instantly Wellington was up and after him.

The French retreat became a flight.

They threw away baggage and ammunition that they might travel the lighter.