This is essentially scene-setting, but very good scene-setting. I had not realised that Roman fleets circumnavigated Great Britain and went the whole way round the Arabian peninsula. Gibbon praises the Roman empire for its lack of military adventurism beyond its borders, though then takes some delight in describing the conquests of Britain (at some length) and Dacia (more briefly). There is then a lengthy description of the military – the army being concentrated on the European frontier, the Danube and Rhine – and then a gazetteer of the entire empire, which I found pretty clear even without a map (though I admit I know the geography fairly well).
Why the Romans didn’t want to conquer Scotland:
The masters of the fairest and most wealthy climates of the globe turned with contempt from gloomy hills assailed by the winter tempest, from lakes concealed in a blue mist, and from cold and lonely heaths, over which the deer of the forest were chased by a troop of naked barbarians.
On Croatia and Bosnia in the present day:
the former obeys an Austrian governor, the latter a Turkish pasha; but the whole country is still infested by tribes of barbarians, whose savage independence irregularly marks the doubtful limit of the Christian and Mahometan power.