that from the 10th to the 19th century some 6,000 to 7,000 slaves were transported north each year. Perhaps as many as nine million slaves were exported along the trans-Saharan caravan route.
The city of Gao was founded around the seventh century as Kawkaw, its first recorded monarch being Kanda, who founded the Za Dynasty of what became the Songhai Empire. He ensured the city’s growth by allowing trans-Saharan traders to visit and Berbers to settle. Trade increased after Za Kossoi converted to Islam in 1009.
The Mali Empire conquered Gao sometime before 1300, but Ali Golon re-established Songhai rule. A distinguished author of the period, Al-Idrissi, described it as a "populous, unwalled, commercial and industrial town, in which were to be found the produce of all arts and trades necessary for its inhabitants."
Mali was a Muslim kingdom, and under it, the gold-salt trade established in the pre-Roman era continued. Other trade goods were slaves, kola nuts from the south, and slave beads and cowrie shells from the north (for use as currency). It was under Mali that the great cities of the Niger River bend—including Gao—prospered.
By the end of the 1460s Sonna Ali Ber, the founder of the Songhai Empire, had taken Djenne and Timbuktu, thus gaining control of some of the principal trading towns of the Sahel. Ali was succeeded by Askia Mohammad I, who defeated the heir in battle in 1493, then consolidated his territorial conquests and introduced Islam as the state religion. The empire flourished for the next hundred years until the Moroccan conquest of 1591.
Askia Mohammed expanded his empire by conquest until it covered an area that stretched over 2,000 miles, from the mouth of the Gambia River in the west to Lake Chad in the east. In the process he established a strongly centralized administration, though in some cases he allowed regional kings to continue ruling as long as they paid tribute. He died in 1528.
During his rule, Gao had about 70,000 residents and a 1,000-boat navy, but Gao was largely destroyed by the Moroccan invasion of 1591. The town remained small until French rule was imposed in the early twentieth century, when the port was expanded. It had a population of 57,978 in 2005.
Other attractions in Gao include the original fourteenth-century Gao Mosque, a museum devoted to the Sahel, markets including a night market, and La Dune Rose, a sand dune named for its appearance at dawn and nightfall.
Gao has an international airport and is linked to other cities along the Niger River, including Timbuktu, by a ferry service. In 2006 a new bridge across the Niger at Gao was inaugurated. While for centuries a transit and trade hub, the tourist industry, especially serving cruises of the Niger, has also become important to the local economy.
Mud either as brick or as pisé is associated with the greatest examples of West Africa's monumental architecture. The area most suited to mud-brick architecture is the savanna, where there is enough water to make bricks, plaster, and pisé (rammed earth) yet not too much rain to dissolve the dried mud walls. Traditionally, rammed earth buildings are common in arid regions where wood is in scarce supply. The traditional methods of mud architecture vary from one town to another; in Djenne cylindrical mud bricks were used, whereas in other towns simple dried-earth lumps were the building material.
Mud architecture lends itself to the creation of plastic sculptural forms on fairly simple structures, thus a simple rectangular facade can be enlivened by the addition of crenellations, engaged pillars, and decorative panels.
The Tomb of Askia is the central commanding feature of the Great Mosque of Gao. This layout pays homage to the Saharan tradition of prominent ancestral tumuli or tomb mounds erected over graves that date to before 1000 B.C.E. This large feature was incorporated into a new mosque building tradition in which the mosque itself becomes a combination of tomb, minaret, and sacred enclosure.
The tomb itself is built on an almost square plan measuring about 14 by 18 meters. The f