267 A University of Geneva, Laboratory Archaeolo- gy and Population in Africa B University of Ghana, Department of Archae- ology and Heritage Studies C Eidgenössische Technische Hochschule Zurich, Laboratory for Ion Beam Physics D Archaeologist, Neuchâtel E Tera, Sion F Office du Patrimoine et de l’Archéologie, Neuchâtel G Archaeologist, Amman H Service cantonal d’archéologie, Geneva I Ghana Museums and Monuments Board J Institut géographique national, Paris SLSA Jahresbericht – Rapport annuel – Annual report 2018 Preliminary Report on the 2018 Season of the Gonja Project (Ghana, Northern Region) Denis Genequand A , Wazi Apoh B , Kodzo Gavua B , Samuel Gyam B , Irka Hajdas C , Déborah Locatelli D , Fabien Maret E , Christian de Reynier F , and Isabelle Ruben G With the collaboration of Marion Berti H , Prince Lawerh I , Edward Nyarko B , and Aurélie Tarrago J 1. Introduction 1. 1 Background of the project This report is about the fourth field season of the Gonja Project, which ran at the beginning of 2018. It was devoted to archaeological excavations and a topographical survey in Old Buipe, and to the architectural study of the mosques of Dondoli in Wa and Babayiri in Gambaga, in the Upper West Region and Northern Region, respec- tively (fig. 1). As a short reminder, the general aim of the Gonja Project is the study of the Isla- misation of Northern Ghana, achieved through an archaeological study of the Gonja state with a particular focus on the spatial organisation, development, and plan of older settlements and their monuments. (For further details about the project, the K ulpāwn S i s il i Lake Volta Gambaga 0 100 km N 1 Fig. 1 Map of Ghana, showing the place names mentioned in the text and the extent of the Gonja state in the 18th century (drawing Marion Berti)