This book is a military organisational history of the Roman Empire on the lower Danube from the emperor Augustus (r. 27 BC-AD 14) to the emperor Severus Alexander (r. AD 222-235). Using a diverse body of evidence, from Roman military diplomas to funerary inscriptions and literary sources, the book looks at changes in troop disposition involving the legions, auxiliary units, the vexillations and the naval units based in Moesia Superior and Inferior, and around the northern and western coasts of the Black Sea. The book also examines the emplacement of the region's units, and contextualises both the disposition of troops and their emplacement in terms of regional strategy and the strategy of the empire as a whole. Besides the discussion and analysis, the book also includes detailed maps of the region and useful tables that summarise the results.