Book XXI of Livy's history of Rome is one of the most frequently read either in its entirety or in extracts, for it includes Carthaginian campaigns in Spain and Hannibal's momentous crossing of the Alps to invade Italy.

P.G. Walsh's edition is designed specifically for use by students at A-Level. The commentary explains points of historical and literary importance, and elucidates grammatical peculiarities and passages of unusual difficulty. The introduction sets Livy in the context of Roman historiography as a whole, and deals in particular with Book XXI. There is a full vocabulary as well as an index of names and illustrative maps and plans.