"The period selected for study starts with the Marian army reforms and ends with the accession of Septimius Severus. My main purpose has been to examine the internal organization of the legions, the areas from which they drew their recruits, and the conditions under which their soldiers served and were discharged. An attempt has also been made to trace the movements of the legions in the first two centuries of the Principate, the circumstances in which new units were raised, and the normal orders of battle and march, while in the introduction the stages by which the army developed in the pre-Marian Republic have been sketched in outline"--Preface.