NEGROLAND AND WESTERN ARABS 89 warning of the approach of a caravan, which messengers from the town were then sent to meet, carrying water into the desert for a four days' march. Without this precaution caravans frequently perished of thirst. Like all great plains in which the mirage is common, this desert had the reputation of being haunted by demons. On the more westerly route, at a distance of twenty days from Sidjilmessa, lay the great salt-mine of Tegazza, which is described in detail by every writer.