Today we are traveling deep into the forests of Germania, back to the year 9 CE, where Rome suffered one of its most shocking defeats. For decades the Roman Empire had marched across Europe, building roads, planting forts, and convincing itself that nothing could stand in its way. But arrogance has a way of blinding even the most powerful empires.

At Teutoburg Forest, three entire Roman legions vanished. They were led by Publius Quinctilius Varus, a governor more comfortable collecting taxes than commanding troops, and betrayed by a man who knew Rome inside and out, the German chieftain Arminius. Over four days of rain, mud, and ambush, the legions were destroyed. When the news reached Augustus, the most powerful man in the world cried out for his lost soldiers.

This is the story of the day Rome learned it was mortal.