Their bones were grinded into fertilizers and their teeth were extracted from their dead bodies to make dentures. Seriously.

"Bones of English Dead at Battle of Waterloo Were Sold as Fertilizer, Study Suggests" https://www.newsweek.com/bones-english-dead-battle-waterloo-were-sold-fertilizer-study-suggests-1718176

The dentures made from the teeth of dead soldiers at Waterloo https://www.bbc.com/news/magazine-33085031

In 1815, dentistry as we know it today was in its infancy - and the mouths of the rich were rotten. So they took teeth for their dentures from the bodies of tens of thousands of dead soldiers on the battlefield at Waterloo.