The Duchy of Warsaw (, , ) was a Polish state established by Napoleon I in 1807 from the Polish lands ceded by the Kingdom of Prussia under the terms of the Treaties of Tilsit. The duchy was held in personal union by one of Napoleon's allies, King Frederick Augustus I of Saxony. Following Napoleon's failed invasion of Russia, the duchy was occupied by Prussian and Russian troops until 1815, when it was formally partitioned between the two countries at the Congress of Vienna. It covered central and eastern part of present Poland and minor parts of present Lithuania and Belarus.