Trade from around 300 CE was conducted by caravans of camels. According to Ibn Battuta, the explorer who accompanied one of the caravans, the average size per caravan was 1,000 camels, but some caravans were as large as 12,000. The caravans would be guided by highly-paid Berbers, who knew the desert and could ensure safe passage from their fellow desert nomads. The survival of a caravan was precarious and would rely on careful co-ordination. Runners would be sent ahead to oases so that water could be shipped out to the caravan when it was still several days away, as the caravans could not easily carry enough with them to make the full journey. In the mid-14th century, Ibn Battuta crossed the desert from Sijilmasa via the salt mines at Taghaza to the oasis of Oualata. A guide was sent ahead and water was brought on a journey of four days from Oualata to meet the caravan.