Sertorius (17.1-17.2)

But of all his military exploits that which he performed in dealing with the people called Characitani is admired as much as any. They are a people beyond the river Tagonius, and they do not dwell in cities or villages, but on a large and lofty hill containing caves and hollows in the cliffs which look towards the north. The whole country at the base of the hill abounds in white clay and a soil that is porous and crumbly; it is not firm enough to bear the tread of man, and spreads far about if only slightly stirred, like unslaked lime or ashes.

These Barbarians, then, whenever they were afraid of war, would hide themselves in their caves, take all their plunder in with them, and keep quiet, for they could not be taken by force; and at the time of which I speak, when Sertorius had retired before Metellus and encamped at the base of their hill, they thought scornfully of him as a vanquished man, and he, either out of anger, or because he did not wish to be thought a fugitive, at break of day rode up to the place and inspected it.