The largest and most important organizational unit of Napoleon's army was the Corps. Literally an army within an army each army corps typically numbered between ten and twenty thousand men depending on available resources at any given time. Each corps contained separate Infantry, Cavalry, Artillery, Supply, Communication and Medical units and were commanded by a Marshal of the Empire.
The purpose of dividing the Grand Army into Corps was to give it greater strategic and tactical flexibility. It was Napoleon's intention during times of both war and peace to ensure that he knew exactly what was going on in Europe. None of his highly mobile Corps were to be more than a couple of hours marching or communication distance from one another, and the ultimate objective in war was for one or more of the Corps, or the Emperor himself of course, to identify the location of a split in allied forces and concentrate all Corps upon that singular objective, achieving superiority in numbers where it counted the most.
When leaving on campaign, resources allowing of course, Napoleon always made sure his army was in tip top shape throughout its structure. Every Platoon, every Company, every Battalion, every Regiment, every Division and every Corps had to be fully ready to march. And it was typical of Napoleon to know all the intricate details of his available forces. His dispatch library is full of letters in which the Emperor remarks on matters concerning his army, a unit that didn't have the right kind of overcoat, another that was undermanned for no apparent reason, another unit that wasn't wearing the proper breeches, or another that wasn't using the right breed of war horse, stuff like that. In one letter, he even accurately remarked on the particulars of an artillery battery situated on the Channel coast facing England which he hadn't even seen in in many months. His memory was incredible.
One of the things for which Napoleon's armies were most famous was their incredible ability to march. More than once their enemies, one of whom was none other than the Duke of Wellington himself, remarked of the French winning a battle `at the cost of bootlaces'. The ability of the French to outmarch opposing armies was something which confounded their enemies time and time again.
There are four good examples of this ability. The first one is seen in the Second Coalition campaign of 1800 when the Army of Italy crossed the Great St. Bernard Pass in the Alps and emerged into the plains of Northern Italy and the Po River valley just prior to the victory at Marengo. This ingenius strategy allowed Napoleon to bear down on Melas' Austrians from behind.
The second example is seen in 1805 during the Third Coalition campaign when after realizing there would be no invasion of England, Napoleon's Grand Army did a 180 degree turn and headed off more than on a 1,200 miles march to deal a blow to the Austro-Russian alliance at Austerlitz.
The third example is seen in the Austrian War of 1809, at the outset of which the Emperor's Guard was still mired in the ugly war in Spain. In March of that year, Napoleon sent orders for his Guard infantry regiments, which he hadn't seen in six months.
By the time the Guard finally made it to Austria to rejoin the Emperor, arriving at his headquarters at Vienna's Schonbrunn Palace for a review on June 7, they had marched 1,750 miles in 75 days to get there, an incredible marching rate of nearly 25 miles per day, no other army in Europe could boast of wearing out its shoes at such a pace.
The fourth example I choose to focus on was the desperate Campaign of 1814 in which the old veterans and the young conscripts alike marched and fought in all directions like madmen in the `Five Days' Campaign' trying to extricate their Emperor from the closing ring of invading allied armies.