Strabo Geography 4.5.3

[3] Divus Caesar twice passed over to the island, but quickly returned, having effected nothing of consequence, nor proceeded far into the country, as well on account of some commotions in Keltica, both among his own soldiers and among the barbarians, as because of the loss of many of his ships at the time of the full moon, when both the ebb and flow of the tides were greatly increased. ¹ Nevertheless he gained two or three victories over the Britons, although he had transported thither only two legions of his army, and brought away hostages and slaves and much other booty. At the present time, however, some of the princes there have, by their embassies and solicitations, obtained the friendship of Augustus Caesar, dedicated their offerings in the Capitol, and brought the whole island into intimate union with the Romans. They pay but moderate duties both on the imports and exports from Keltica; which are ivory bracelets and necklaces, amber, vessels of glass, and small wares; so that the island scarcely needs a garrison, for at the least it would require one legion and some cavalry to enforce tribute from them; and the total expenditure for the army would be equal to the revenue collected; for if a tribute were levied, of necessity the imposts must be diminished, and at the same time some danger would be incurred if force were to be employed.