Warhammer Estalia concept art: Knights of the raging bull

The lands of Estalia accommodate large herds of bulls and cows, and the former are famous throughout the old world for their bad tempers and habit of charging anything that gets too close. The bad temper of these creatures reaches such a point that the Estalians have the stupid idea in the eyes of the rest of the nations of the old world of trying to train the largest of these creatures for war, an act that has claimed almost as many casualties of their caretakers as enemies. Still, it's hard to deny that a herd of raging bulls is a terrifying sight on the battlefield, these creatures weighing nearly a ton will shake the ground as they run, crushing bone and armor wherever they pass, leaving only wails behind and cries of pain.
The bravest or the most foolish among the Estalian knights try to use the greatest bulls as war mounts. Many are killed by their beasts before making even the slightest progress in taming, but those who do have gained a fearsome mount indeed. So much does it increase the combat capabilities of these knights that many often earn small fortunes, which most spend on the best armor and barding for their bulls that dwarf smiths are willing to sell them. Thus, extremely armored, the knights of the raging bull are capable of charging directly against a wall of spears or halberds, enjoying the expressions of terror that their enemies make when they see how their spears break and the halberds bend in front of the dwarven steel and the hard bodies of pure muscle of the bulls.