Tacitus.

Who remains one of the world's great historians. Sometimes we read old books because we want to understand how these books influenced the course of thought. But sometimes, old books are just genuinely good in their own right and would be just as good if published today: Aristotle, Thucydides, Tacitus, Aeschylus, and a bunch of other authors fit this latter mold. I wish more people read them.

But in this case I preferred Caesars book about the battle. Caesar had a very clear and engineer-like writing style, compared to Tacitus.