Final answer:
Gao was the city that Malians would have to pass through to trade with the southern coast. It served as an important trading center in West Africa, facilitating the trade of various goods.
Step-by-step explanation:
The city that Malians would have to pass through to trade with the southern coast is Gao. Gao was an important trading city in West Africa, located at the eastern edge of the Niger bend. It served as a key link in the trans-Saharan trade route, facilitating the trade of gold, copper, enslaved captives, and salt in the region. Gao's strategic location made it a vital trading center for Malians seeking to trade with the southern coast.