When the Adjutant General’s Office published Raphael Thian’s notes on U.S. military geography in 1880, it produced an invaluable research tool for generations of military historians to come. In this single documented reference volume, Chief Clerk Thian traced the confusing mutations through which the divisions, departments, and districts of the Army’s command had evolved since 1813. The volume is divided into three parts, beginning with the names of the United States Army Continental Commands, the date and authority for their creation, location of the headquarters, geographical changes and discontinuances, and other details including the geographical boundaries embracing each division, department, and district. Part II is filled with background information on states and territories, and Part III lists the maps contained in The Military Atlas of the United States. The Addenda to this edition expand and update Thian’s work. Notes made by Francis B. Heitman to keep his personal copy current are included, as is the Memorandum published by the government in 1906. This addition lists all changes from 1898 through 1905.