We hear a lot about the names Timbuktu and Swahili city-states, but less about the cities themselves. How important were urban centers in medieval and early modern sub-Saharan Africa?

Interesting question!

To start off, I think the question can be answered in two ways. The first would be a straightforward approach that discusses what the role of cities were in different African pre-colonial societies, and how they were important within that society and in diplomatic/trade/tributary interactions between societies.

The second way would be a more theoretical and historiographical answer which seeks to answer what a city is and does, why Africanists are and have been interested in urbanism, and asks whether this is appropriate or if interest in cultures/societies that are organized into bands/segmentary societies and Chiefdoms/middle-range societies are equally important to arriving at a holistic understanding of the African past.

I'll start off tackling the theoretical/historiographic part, and will maybe tackle the historical examples in a later post.

The Theory and Historiography of the African City

What even is a city? Why do we care about them?

Defining what a city is, is a crucial first step. What distinguishes a village from a town from a small city? Is it simply a matter of population size? does a Town become a city once it hits 5,000 inhabitants? 10,000? Or is a city defined by physical structures like a defensive wall or a marketplace or a mosque or palace/courthouse? A university? Monuments?

Not so much.

In the 1950s and 1960s, historians and arcaeologists tended to rely on such a "features checklist" approach, and modeled what a city should look like on observed examples from Mesopotamia or the Classical mediterranean, and understanding cities in terms of a political/governmental context of exerting state control.

However, with more fieldwork in West Africa, a new generation of Africanist Archaeologists starting in the 1970s moved away from that emphasis on political/governance control, based on the observed developments of sites like Dhar Tichitt and Djenne Djenno, which lacked the signs of monumental architecture or administrative structures that would indicate a strong state/royal control.

Rather, Africanist archaeologists/anthropologists lean towards a more economic approach. In this view, cities exist as a nexus for the surrounding countryside. The flow of resources from the countryside into the city which enables the feeding of the population, also allows for greater differentiation of craft specialization.

So, in this newer, looser definition, a city/urban center would differ from a village or a town by both having a larger (indeterminate) population, but also by having a greater number and diversity of specialist jobs (i.e. merchant, blacksmith, legal scholar, glassblower, etc.)

As a corollary to this definition, a city has greater commercial significance than towns or villages, both because of that larger population as well as the larger pool of skilled labor. So, cities often served as important destinations or entrepots for long distance trading networks (e.g. Timbuktu, Gao, Kilwa or Mombasa). So, archaeologists like to excavate urban sites because they tend to be archaeologically visible sites that can give a picture of what sort of trade connections and economic activity was happening.

Now, on the other hand, there are urban sites in pre-colonial africa that do show examples of monumental architecture (e.g. Aksum, Lalibela, Meroe, Great Zimbabwe, Swahili states) or walls (Hausa cities) or palaces/religious structures (e.g. Ambohimanga, Abomey, Ile Ife).

So, can you understand African history more broadly if you understand the history of their city? Are cities "important"?

The relative population density of pre-colonial cities, and the economic/social differentiation of the populations in them, ipso facto requires a highly complex society.

Unhappily, the intellectual legacy of colonialism has left many people with myths that Africa prior to European conquest was lacking in cities, empires, or innovation. That African societies did not "develop" to the levels that European or Asian civilizations did.

So, looking at African cities (and the study of empire) does help to counter-act such myths, and show Africans were capable of social complexity.

On the other hand, focusing solely on cities and empires/kingdoms does run the risk of falling into what Ann Stahl calls the "trevor-roper trap". That is, by pointing to cities and extensive empires as evidence to counter myths of "lack of development" scholars risk failing to question the presuppositions of the "developmentalist" narrative (i.e. that Cities and complex societies are "better" than chiefdoms, which are "better" than bands).

Cities can be important, and are good to study, but a holistic understanding of Africa must account for chiefdoms/middle range societies as well as pastoralist nomadic clan-based societies, and rainforest and desert hunter-gatherer-fishermen.