The First Western Army was created in 1810 as part of the reorganisation of the Imperial Russian Army, and was intended as a defense against the north-western part of the Empire from the expected invasion by Napoleon. The total troops in this Army included 150 battalions, 128 squadrons, 19 cossack regiments, and 590 guns.
The command-in-chief of the First West Army on March 19 (April 2) 1812 was assigned to General of the Infantry M. B. Barklay de Tolli. However, after arriving 14 (26) April 1812 in Vilno at the general headquarters of the First West Army, the Emperor Alexander I became both legally and actually its commander-in-chief, since according to §18 of "Establishments for management of the large acting army”, introduced on January 27 (8) February 1812, “the presence of Emperor represents the main command authority of the army, unless when specified by an order, the acting commander-in-chief is directed to retain complete authority”. There was no such order, therefore, the Emperor assumed command of the army. When on the 7 (19) July 1812 the Emperor left the field army, M. B. Barklay de Tolli again became its commander-in-chief.[1]