Neque enim temere praeter mercatores illo adit quisquam, neque eis ipsis quidquam praeter oram maritimam atque eas regiones quae sunt contra Gallias notum est. itaque vocatis ad se undique mercatoribus neque quanta esset insulae magnitudo, neque quae aut quantae nationes incolerent, neque quem usum belli haberent aut quibus institutis uterentur, neque qui essent ad maiorum navium multitudinem idonei portus, reperire poterat.
(Caesar, De Bello Gallico 4.20)
In fact, nobody except traders journey thither without good cause; and even traders know nothing except the sea-coast and the districts opposite Gaul. Therefore, although he summoned to his quarters traders from all part, he could discover neither the size of the island, nor the number or the strength of the tribes inhabiting it, nor their manner of warfare, nor the ordinances they observed, nor the harbours suitable for a number of large ships. (tr. Henry John Edwards)
Crambe Repetita 