Arab geographers pictured the Sahara as a sea of sand, and they named its southern edge accordingly. The word Sahel comes from the Arabic for "shore": the grassland and savanna belt where the desert crossing ended. Along this shore, between about AD 800 and 1600, rose three great empires in turn, Ghana, Mali and Songhai, each built on control of trade and each remembered today in the names and pride of modern nations.

The trade that built empires

Camels, in wide use in the Sahara by the early centuries AD, made regular caravans across the desert possible. Traders from North Africa brought cloth, copper, horses and books south. The Sahel had something the Mediterranean world craved: gold, mined in fields near the upper Senegal and Niger rivers and later in the Akan forests. The desert had something the Sahel needed: salt, cut in slabs from mines deep in the Sahara. At the heart of trans-Saharan commerce was gold from the south traded for salt from the desert. Whoever controlled the meeting points could tax both.

Ghana

The first of the empires was founded by Soninke people, who called it Wagadu; "ghana" was a title of its king, which Arab writers used for the whole state. Ancient Ghana lay several hundred miles northwest of the modern country, in what is now Mauritania and Mali; modern Ghana borrowed the name at independence as a symbol of African greatness. The fullest description comes from the scholar al-Bakri, who wrote in 1068 in Muslim Spain, never visited, and relied on merchants' reports. Al-Bakri reported that the king kept all gold nuggets for himself and left gold dust to the people, a way of keeping gold scarce and its price high. Ghana weakened in the late eleventh century. Arab sources say the Almoravids, a Berber religious movement, conquered it around 1076, but some historians doubt a conquest took place.

Mali

Mali grew from the Mande heartland on the upper Niger. Its founding hero, Sundiata Keita, is the subject of a great oral epic still performed today. Around 1235 Sundiata defeated Sumanguru Kante, king of Sosso, at the battle of Kirina, and his successors, who took the title mansa, built an empire larger than Ghana that controlled the gold fields directly. Mali's most famous ruler, Mansa Musa, made the pilgrimage to Mecca in 1324. The Cairo writer al-Umari reported that Musa's lavish spending lowered the value of gold there for years afterward. In 1375 a Catalan atlas made in Majorca showed him enthroned, holding a golden orb, a sign of how far his fame traveled.

Timbuktu

Timbuktu, near the bend of the Niger, began as a seasonal camp and became a center of trade and Islamic learning. Under Mali and Songhai its mosques, including Djinguereber and Sankore, drew scholars of law, grammar, theology and astronomy, and families built private libraries of manuscripts that they guarded for centuries. Its most famous scholar, Ahmad Baba, wrote a legal opinion in 1615 on who could lawfully be enslaved. Ahmad Baba argued that dark skin was no legal ground for enslaving anyone; in his view only unbelief could justify it, so he rejected the racial idea that Black Africans were natural slaves while still accepting the enslavement of non-Muslim captives.

Songhai

Songhai, centered on the city of Gao downstream, broke away from a weakening Mali. Sunni Ali, who ruled from 1464 to 1492, took Timbuktu in 1468 and built a fighting state around river fleets and cavalry. Askia Muhammad seized power in 1493, made his own pilgrimage to Mecca, and organized provinces and officials. Songhai became the largest of the three empires. Its end came suddenly. In 1591 a Moroccan army armed with firearms crossed the Sahara and defeated Songhai at Tondibi. The invaders could not hold the whole empire, but the damage lasted; Ahmad Baba himself was deported to Marrakesh. Other powerful states, such as Kanem-Bornu near Lake Chad, the Hausa cities, Oyo and Benin, flourished in the same centuries.

Worked example: weighing Mansa Musa's pilgrimage

Few events in African history are better known than Musa's journey, and few are wrapped in more exaggeration. Popular accounts claim tens of thousands of followers and hundreds of camels laden with gold. What can a historian actually say?

The key written source, al-Umari, wrote in Cairo about a dozen years after the visit and interviewed officials who had met Musa, which makes him close to events, though dependent on hearsay and keen to impress readers. He says Musa gave away so much gold that its price in Cairo fell, and that the mansa ran short on the way home and had to borrow from merchants. The Catalan atlas shows what Europeans believed, not what happened. Mande oral traditions, meanwhile, remember Musa less warmly than Sundiata, and some versions criticize him for spending Mali's wealth abroad.

The careful conclusion is that the pilgrimage was real, spectacularly expensive and widely reported, while specific numbers are guesses. It was also diplomacy. Musa returned with scholars and an architect, linked Mali to the wider Muslim world, and announced to Cairo, and through Cairo to Europe, that a great kingdom lay south of the Sahara.