17 September 2026 marks 217 years since the Treaty of Fredrikshamn, known in Finnish as the Treaty of Hamina. The 1809 printed text held by the National Library of Finland carries the double date 5/17 September: 5 in the Julian calendar, 17 in the Gregorian calendar used today.

The agreement between Sweden and the Russian Empire ended the Finnish War of 1808–1809, fought within the Napoleonic Wars. After Sweden did not join Napoleon’s Continental System against the United Kingdom in full, Russian forces gradually occupied the Finnish territories then under the Swedish crown.

Under the treaty Sweden ceded to Russia, among other lands, the Finnish provinces, the Åland Islands and a northern belt as far as the Torne–Muonio line. The territories were organised as the autonomous Grand Duchy of Finland under the Russian emperor. Alexander I had promised to preserve local religion, laws and privileges; the extent of autonomy varied through the nineteenth century.

For Sweden, the loss of Finland was among the largest territorial changes in its history. Swedish remained an important language in the new structure. Institutions developed in the autonomous period later contributed to the modern Finnish state, which declared independence in December 1917 after the Russian Revolution.

The treaty should not be read as the instantaneous birth of contemporary Finland. It is a peace instrument that ended Finland’s Swedish era and opened the autonomous period inside the Russian Empire, with borders and rights set out in the articles signed at Hamina.

Two hundred and seventeen years later, the document remains a landmark in Nordic history: the end of a war, a territorial cession and the start of a political status that lasted until 1917.

Image: Pitkäkaula, fortress walls at Hamina. Wikimedia Commons, CC BY-SA 3.0. Not a facsimile of the treaty. Cropped to 16:9.

Source consulted: National Library of Finland — Freds fördrag … Fredricshamn, 5/17 september 1809; Encyclopaedia Britannica — Finnish War.