Charleroi lay on the north bank of the Sambre River. Since its construction began in 1666, its purpose had been to watch the crossings of the Sambre into France. Thus, the southern side of the fortress was extremely strong, with its reinforced lower town extending deep into floodable meadows, while its walls overlooked the Sambre. The defenses to the north were comparatively weak, and the ground rose gradually through woodland.
But after a siege in 1794, Charleroi's defenses began to fall into disrepair. Jourdan and Kléber had commanded the defense at the time, while Prince of Coburg of Austria had led the attack.
It had been a hard-fought battle. Although the French army had ultimately prevailed, its casualties had been severe. This small town had only five thousand residents in total and simply could not provide provisions for seventy thousand men. It had prospered through coal, and it also had clothing and glassware factories, but coal was the region's pillar industry. Vast quantities of coal were mined from the surrounding woods, and the town's principal trading partner was France, so the only language used locally was French.
Once the fighting ended, the soldiers left, but the locals still had to go on living. A country road paved with gravel ran from Charleroi to Brussels. Coal wagons often traveled along it, turning the road black. The coal supplied not only Brussels's residents but also its industries. The route passed through a small town called Waterloo, located in a hollow between hills, where the north-south road crossed an ancient Roman road running east to west. That road was almost perfectly straight.
After so many years, the old Roman road could barely still be used, but the gravel road became extremely difficult whenever it rained. The coal dust scattered across it clumped together