Trans-Saharan trade is trade between sub-Saharan Africa and North Africa that requires travel across the Sahara. Though this trade began in prehistoric times, the peak of trade extended from the 8th century until the early 17th century CE. The Sahara once had a different climate and environment. In Libya and Algeria, from at least 7000 BCE, pastoralism (the herding of sheep and goats), large settlements and pottery were present. Cattle were introduced to the Central Sahara (Ahaggar) between 4000 and 3500 BCE. Remarkable rock paintings (dated 3500 to 2500 BCE) in arid regions portray flora and fauna that are not present in the modern desert.
As a desert, the Sahara is now a hostile expanse that separates the Mediterranean economy from the economy of the Niger River Basin. As Fernand Braudel points out, crossing such a zone, especially without mechanized transport, is worthwhile only when exceptional circumstances cause the expected gain to outweigh the cost and the danger. Trade was conducted by caravans of camels. According to Maghrebi explorer Ibn Battuta, who once traveled with a caravan, an average one would amount to 1,000 camels, but some caravans were as large as 12,000. The caravans were guided by highly-paid Berbers, who knew the desert and could ensure protection from fellow desert nomads. The caravans' survival relied on careful coordination: runners would be sent ahead to oases for water to be shipped out to the caravan when it was still several days away, as the caravans could usually not carry enough to make the full journey. In the mid-14th century CE, 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 over a four-day journey from Oualata to meet the caravan.
