The Danube Legion (Polish: Legia Naddunajska; or the Rhine Legion - French: Legion du Rhine) was a unit of Poles in the service of Napoleonic France. It was also known as the 3rd Polish Legion.
It was formed on 8 September 1799 in the Batavian Republic from Polish volunteers, mostly French prisoners of war from the Austrian Army. Numbering about 6,000 the legion was commanded by general Karol Kniaziewicz.
The legion fought at the Battle of Marengo and Battle of Hohenlinden. However during treaty negotiations between the French and the Austrians, the French were finding the Polish issue to be a problem; the Poles wanted the French to continue fighting against the partitioners of Poland; the future Polish national anthem, Mazurek Dąbrowskiego, created by Józef Wybicki, promised 'the return of the Polish army from Italy to Poland'. Instead, the French used Polish troops to quell down uprisings in conquered territories, which led to much unrest amongst the Polish troops. The prospect of being assigned to Louis I of Etruria, Napoleons appointee as the King of Etruria did not sit well with their republican sympathies. As the King also felt reluctant to take financial responsibility for them, Napoleon reassigned them to quell the Haitian Revolution which was currently giving him problems. General Jan Henryk Dąbrowski initially complained from his headquarters in Milan, but subsequently acquiesced. After Stanisław Fiszer had turned down the command in favour of returning to Poland, Fortunat Bernard, a Frenchman, was appointed. After a storm had thwarted an initial attempt to depart, the 3rd Polish Demibrifrade left Livorno on May 17, 1802, recahing Cadiz by July 11. It was here that Bernard applied to the French government that the demibridae be reassigned as a French demibrigade of the line. The fleet set sail again on July 24, and it was only at this stage that many of the Poles were informed that they were bound for Haiti.