C. Julius Caesar, Gallic War

Caesar, being informed of these things by Crassus, since he was so far distant himself, orders ships of war to be built in the mean time on the river Loire , which flows into the ocean; rowers to be raised from the province; sailors and pilots to be provided. These matters being quickly executed, he himself, as soon as the season of the year permits, hastens to the army. The Veneti, and the other states also, being informed of Caesar's arrival, when they reflected how great a crime they had committed, in that, the embassadors (a character which had among all nations ever been sacred and inviolable) had by them been detained and thrown into prison, resolve to prepare for a war in proportion to the greatness of their danger, and especially to provide those things which appertain to the service of a navy, with the greater confidence, inasmuch as they greatly relied on the nature of their situation. They knew that the passes by land were cut off by estuaries, that the approach by sea was most difficult, by reason of our ignorance of the localities, [and] the small number of the harbors, and they trusted that our army would not be able to stay very long among them, on account of the insufficiency of corn; and again, even if all these things should turn out contrary to their expectation, yet they were very powerful in their navy. They well understood that the Romans neither had any number of ships, nor were acquainted with the shallows, the harbors, or the islands of those parts where they would have to carry on the war; and the navigation was very different in a narrow sea from what it was in the vast and open ocean. Having come to this resolution, they fortify their towns, convey corn into them from the country parts, bring together as many ships as possible to Venetia , where it appeared Caesar would at first carry on the war. They unite to themselves as allies for that war, the Osismii, the Lexovii, the Nannetes, the Ambiliati, the Morini, the Diablintes, and the Menapii; and send for auxiliaries from Britain, which is situated over against those regions.