These were the dispositions of the Allies; but they were not strategically in a sound position. Wellington’s line of supply lay through Ostend and Antwerp to the sea; Bluchers lay by Liège and Maestricht to the Rhine. Therefore, in the event of a disaster to either, or both, their lines of retreat would carry them further apart. It was this weakness on which Napoleon based his whole plan. The Prussian army, being the nearer to Napoleon, would be the first met with, and therefore the first to concentrate. By a rapid crossing of the Sambre at Charleroi, Napoleon would force the First Corps back on Fleurus, where the Prussian army was to concentrate, and throw himself on the point of junction of the Allied armies when concentrated; namely, the Quatre-Bras-Sombreffe road. He knew that the Prussians, by reason of their dispositions, would be concentrated first, and he therefore hoped, by possessing himself of the point of junction, to beat their concentrated army before Wellington, who, he decided, would be much slower in assembling his troops, could come up to Quatre-Bras. It was of vital importance to Napoleon to beat the Prussian army, entirely and completely, in its position at Sombreffe, before Wellington could come to Blucher’s assistance. The retreat of the Prussians on Wavre without such a decisive defeat, would have upset the whole plan: for Wellington would then have retired and united with Blucher, either in front of Brussels or behind it. But, if thoroughly beaten, the Prussians would retreat on Liège: and only in this way could Napoleon effectually separate the two armies and crush them in turn. Such was Napoleon’s argument. In conception, the plan was brilliant; but its execution was unworthy of him. _Composition of the French Army._