The Indispensable booklist

[Paullus Scipio]

Here's a few that I have enjoyed, and which might be considered indispensable :-
"The Army of the Caesars" Michael Grant - covers the relationship between Army and Society, its role as 'king-maker', a general history of the army in context.
Pretty much anything by Michael Grant is well worth reading - for a general history, his "History of Rome" is hard to beat.
"The Roman Imperial Army" Graham Webster - a detailed look at the army of the first and second centuries A.D.
"Hannibal's War","The first Punic War" and "The Spartan Army" and anything else by J.F. Lazenby.

And for those looking to gain a perspective on Late Romans:-
"The Later Roman Empire 294-602 A.D." - A.H.M Jones
"The Fall of the Roman Empire - a Reappraisal" - Michael Grant (again!)
"The Fall of the Roman Empire -the military explanation" - Arthur Ferrill
Finally ( for now!!),
"Generallisimos of the Western Roman Empire" - John Michael O'Flynn - a look at the role of Arbrogast, Stilicho, Constantius, Aetius and Ricimer and Odovacer in the break-up and evolution of the Western Empire