revolutionary activity extended more deeply into the social fabric. In early July 1848, Prussian and Bavarian troops invaded the Bodensee region, and imposed a form of military rule; several important personages, including the Überlingen's physician and one of its schoolteachers, drew lengthy prison sentences for their revolutionary activity, nine months and a year, respectively. One of the former abbeys served as a prison for revolutionary convicts. Two companies of Prussian troops, approximately 400 men plus their officers, occupied the city until late 1850 when they were replaced by ducal troops. Although no sons of Überlingen fought in the Civil War with Austria (Austro-Prussian War), Baden preferring to remain outside the conflict, 72 of Überlingen's young men were called to fight the war with France in 1870; three of them fell in action and are commemorated in the parish church, St. Nikolaus. From 1846 to 1910, approximately 300 Überlingen sons and daughters emigrated to Switzerland, North or South America, or Australia. Überlingen as a spa The healing properties of the city's mineral waters, which sprang from a source under one of the towers on the western side of the city wall, had been understood since the early 16th century, and produced a regular source of income for the city and the spital; during the Thirty Years' War the spring had been covered over; it remained covered in the post-war period and then was largely forgotten. It was fortuitously "rediscovered" during Überlingen's difficult times. A spa hotel was constructed and the notables started to arrive: Heinrich Zschokke (1771–1848), Ludwig Uhland, the poet (1787–1862), Gustav Schwab (1792–1850) and the Germanist Franz Pfeiffer (1815–1868) were regular visitors. A pathway along the western wall, to the highest point within the city gates is still called the Uhland walkway and a marker notes that this was one of the poet's favorite walks. The economic problems were in large part due to the difficulties of transportation. Although the first coal powered steam ship, the Hohentwiel (named for the impregnable castle on the dormant volcano Hohentwiel by Singen), owned by Joseph Cotta, had traversed the Lake in 1825, it was not until 1895, with the construction of a railway link to Überlingen, that the city emerged from its economic difficulties as a spa city. In 1901, the link was connected through Friedrichshafen, making travel to and from the city easier and quicker, and improving the city's prospects as