Given the question: Question: "Where did Napoleon build his force?"  Context: "Before the formation of the Third Coalition, Napoleon had assembled an invasion force, the Armée d'Angleterre, around six camps at Boulogne in Northern France. He intended to use this invasion force to strike at England. They never invaded, but Napoleon's troops received careful and invaluable training for future military operations. The men at Boulogne formed the core for what Napoleon later called La Grande Armée. At the start, this French army had about 200,000 men organized into seven corps, which were large field units that contained 36 to 40 cannons each and were capable of independent action until other corps could come to the rescue. A single corps properly situated in a strong defensive position could survive at least a day without support, giving the Grande Armée countless strategic and tactical options on every campaign. On top of these forces, Napoleon created a cavalry reserve of 22,000 organized into two cuirassier divisions, four mounted dragoon divisions, one division of dismounted dragoons, and one of light cavalry, all supported by 24 artillery pieces. By 1805, the Grande Armée had grown to a force of 350,000 men, who were well equipped, well trained, and led by competent officers."  Answer:
The answer is:
Boulogne