Robert Hughes' Rome

Roman helmet

What about defense?  On the collective level of the army on the march, the Romans displayed unique fortitude and energy in self-protection.  Knowing that "barbarians" in occupied territories were likely to attack at night, when the Roman invaders were tired from the day's exertions and darkness was likely to favor confusion and panic, the Romans did not end their day's labor at the finish of each day's march.  They first put up a camp: not a mere array of tents, but a fully fortified square castrum or encampment, almost an overnight town, with a wall, a ditch (produced by digging up the earth to throw up the wall), and everything that was necessary to protect the mass of troops.

Rome, A Cultural, Visual, and Personal History by Robert Hughes

Reading Hughes' Rome has been a pleasure. The details, like the excerpt above, makes for a very interesting read.  The Roman legions have always fascinated me, and these accounts really catch not only one's interest, but also one's sense of imagination--even wonder.  Further on in the same paragraph, there is a discussion of the severe punishment, which included banishment, of the sentry who fails in his duties.  To imagine the discipline and ultimate commitment of these soldiers makes the story of the disappearance of the Ninth Roman Legion beyond Hadrian's Wall in Roman Britain even more mysterious and thought-provoking.  It's these insights that really give this book its rich character; it's conveying a history less about mere dates and more about important people and practices.

Surprisingly, this book created some early controversy regarding excessive factual errors.  For more information, see this article.