Battle of Barro Vermelho
1838 CE.
Shown on the map at -29.965°, -52.364°.
The Battle of Barro Vermelho, also known as the Battle of Rio Pardo, was an engagement of the Ragamuffin War fought in April 1838. Around 5,000 men were present in the field, an atypically large number for the conflict; the battle was one of the rebels' most important victories during the war.
Text from the Wikipedia article Battle of Barro Vermelho, licensed CC BY-SA 4.0.