The Army of Mainz (Armée de Mayence) was a French Revolutionary Army set up on 9 December 1797 by splitting the Armée d'Allemagne into the Armée de Mayence and the Armée du Rhin. Part of it split off on 4 February 1799 to form the armée d'Observation, though part of the armée d'Observation then re-merged into the Armée de Mayence on 28 March that year (with the remainder forming the Armée du Danube).