#27878 Jean Baptiste Édouard Detaille (1848-1912)

The picture has something of this: cavalry, sword, warrior, knight, seated, people, rider, armor, saddle, horseback, weapon, shield, skirmish, man, equestrian, military, helmet, mammal.
Perhaps it’s a painting of a man riding on the back of a brown horse in front of a large group of men in uniforms on the other side of a field.