BACKGROUND
In 1807 Napoleon had defeated all enemies of the continent and had decreed the continental blockade to British commerce. Only Portugal refused to cooperate with the blockade. Napoleon and Godoy signed in October 1807 Treaty of Fontainebleau, by which Spain allow the passage of French troops in order to invade Portugal, Spain collaborate in the invasion in exchange for territorial concessions. Over 100,000 French soldiers crossed the spanish border road to Portugal, leaving strong garrisons at strategic points along the route.