Two emperors met on a raft moored in the middle of the Niemen River on June 25, 1807, and what they agreed there shocked every European court. On July 9, Napoleon Bonaparte signed the second Treaty of Tilsit, the accord with Prussia, completing a diplomatic revolution that followed his crushing victories at Jena and Friedland. Prussia surrendered nearly half its territory, losing all lands west of the Elbe and its Polish acquisitions, which Napoleon reconstituted as the Kingdom of Westphalia and the Duchy of Warsaw. France and Russia became nominal allies, with Tsar Alexander I agreeing to join the Continental System and choke off British trade. The treaty handed Napoleon unchallenged dominance over continental Europe, yet planted the seeds of his downfall: Russia's eventual abandonment of the blockade drove him to launch his catastrophic 1812 invasion. Tilsit stands as the high-water mark of Napoleonic power, a reminder that empires built on coercion carry their own unraveling within them.