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).
The original article can be found at Army of Mainz and the edit history here.