
The Battle of the Teutoburg Forest saw a Roman army under Publius Quinctilius Varus annihilated by a coalition of Germanic tribes led by Arminius. Roman forces were stretched through difficult forest terrain and ambushed over several days.
The disaster permanently changed Roman ambitions in northern Europe. Instead of expanding deep into Germania, Rome stabilized its frontier near the Rhine, making Teutoburg one of the most consequential defeats in imperial Roman history.
Reference:
TaskLoco™ — The Sticky Note GOAT