[4] Brooding upon what he saw as the humiliation of his native land by Napoleon, Jahn conceived the idea of restoring the spirits of his countrymen by the development of their physical and moral powers through the practice of gymnastics.

[2] The first Turnplatz, or open-air gymnasium, was opened by Jahn in Hasenheide in the south of Berlin[5] in 1811, and the Turnverein (gymnastics association) movement spread rapidly.

[2] In early 1813 Jahn took an active part in the formation of the famous Lützow Free Corps, a volunteer force in the Prussian army fighting Napoleon.

After the war, he returned to Berlin, where he was appointed state teacher of gymnastics, and he took on a role in the formation of the student patriotic fraternities, or Burschenschaften, in Jena.

[4] While at Freyburg, he received an invitation to become professor of German literature at Cambridge, Massachusetts, which he declined, saying that "deer and hares love to live where they are most hunted.

[4] Jahn popularized the four Fs motto "frisch, fromm, fröhlich, frei" ("fresh, pious, cheerful, free") in the early 19th century.

[citation needed] Other memorials to Jahn are located in Groß-Gerau, Germany; Vienna; and Cincinnati, Ohio's Inwood Park in the Mount Auburn Historic District.

He advocated that the German states should unite after the withdrawal of Napoleon's occupying armies and establish a democratic constitution under the Hohenzollern monarchy, which would include the right to free speech.

[12]: 234  Alfred Baeumler, an educational philosopher and university lecturer who attempted to provide theoretical support for Nazi ideology (through the interpretation of Nietzsche among others) wrote a monograph on Jahn[13] in which he characterized Jahn's invention of gymnastics as an explicitly political project, designed to create the ultimate völkisch citizen by educating his body.

[12]: 240–41 Jahn gained infamy in English-speaking countries[citation needed] following the publication of Peter Viereck's Metapolitics: The Roots of the Nazi Mind (1941).

[14] Viereck claimed Jahn was the spiritual founder of Nazism who inspired early German romantics with anti-Semitic and authoritarian doctrines, influencing Wagner and finally, the Nazis.