The subject in this, Number 58 of the series of Cambridge Monographs in African Archaeology, is the range of fortifications on the East African coast. The author traces the development of defences from the 10th to the 19th centuries, from the beginnings of Islamicisation and the apogee of the city-states, to Portugese and Ottoman rule. This broad approach encompasses the main features of military architecture and its interaction with urban societies. As well as defensive structures, the Swahili sites also symbolise urban and non-military use. These appeared from the 10th century, a period where the employment of stone architecture became common. The Swahili centres have both a synchronous and diachronic value; they are witnesses to the political and economic relationships between contemporary settlements, and represent the evolution of urban living. Forts and fortifications reflected royal power, and their study provides a political dimension that affords an insight into the complex relations between the different city-states along this dynamic and vast coastline. The military edifices reflect the periodic tensions and grand events that have shaped the history of the African east littoral.