The Frontiers of Imperial Rome, by David J. Breeze.
The Frontiers of Imperial Rome, I thought, was supposed to be the first analysis of Roman border policy since David Luttwak's classic The Grand Strategy of the Roman Empire. Based on my first skim, that is not the case, which is somewhat disappointing. Breeze's book is not on border policy per se, but on the borders themselves, as in the fortifications.
And on that, it looks impressive. Oodles of diagrams, charts, maps and plans. Lotsa technical stuff. Should be a fun read.