Daugavpils Fortress, also known as Dinaburg Fortress, is an early 19th century fortress in Daugavpils, Latvia. It is the only early 19th century military fortification of its kind in Northern Europe that has been preserved without significant alterations. The construction of the fortress began in 1810 by decree of Tsar Alexander I of Russia, in the atmosphere of increased tension before Napoleon's invasion of the Russian Empire in 1812. Construction of the fortress, due to Napoleon's invasion, lengthy delays, serious floodings and slow construction work, was fully completed only in 1878.