At Napoleon's request he undertook an account of the ancient monarchy of France, which should serve as a justification for the empire. After four years' labor Montlosier submitted his work to a specially appointed committee, by which it was rejected because of the stress laid on the feudal limitations of the royal authority. The work "De la monarchie française . . . ou recherches sur les anciennes institutions françaises . . . et sur les causes qui ont amené la revolution . . ." appeared in 1814 in three volumes, a fourth and supplementary volume in the next year containing a preface hostile to Napoleon.