Sertorius (17.3-17.4)

There was no attacking it anywhere, but as he was wandering about to no purpose and indulging in empty threats, he saw that dust from the soil which I have described was being carried up against the Barbarians in great quantities by the wind. For the caves, as I have said, faced the north, and the wind which blows from that quarter (some call it Caecias) is the most prevalent and the strongest of the wind in that country, being a confluent of winds from watery plains and snow-covered mountains; and at this time particularly, which was the height of summer, it was strong, was fed by the melting snows of northern regions, and blew most delightfully with continual refreshment for man and beast all day.

So, reflecting on these things and getting information about them from the natives of the country, Sertorius ordered his soldiers to take some of the loose and ashy soil that I have described, carry it directly opposite the hill, and make a heap of it there. This the Barbarians conjectured to be a mound raised for assaulting them, and jeered at their enemy.