High Quality Content by WIKIPEDIA articles! Johann von Klenau (13 April 1758 – 6 October 1819), also called Johann Josef Cajetan von Klenau und Janowitz, the son of a Bohemian noble, was a field marshal in the Habsburg army. Klenau joined the Habsburg military as a teenager and fought in Austria`s wars with the Ottoman Empire, the French Revolutionary Wars, and commanded a corps in several important battles of the Napoleonic Wars.