Originally a fortress city, Ingolstadt is enclosed by a medieval defensive wall. The Bavarian fortress (1537–1930) now holds the museum of the Bavarian army. During World War I, future French president Charles de Gaulle was detained there as a prisoner of war. A sappers' drill ground lies next to the river, and two military air bases are located nearby, one used for testing aircraft. The long military tradition of the city is reflected in today's civil and cultural life. Former "off-limit" military training areas have been converted into well-used public parks.