By combining carbon-14 dating of mortar, rereading known written sources and both archaeological and formal analysis, the construction history of the Gothic church of Our Lady in Tongeren can be thoroughly revised. Numerous similarities with religious architecture in Lorraine, the Rhineland, and the Meuse valley reveal the architectural historical significance of Our Lady’s church on the western fringe of the Holy Roman Empire. Inside the church, differences in design are related to the separate spaces used by canons, parishioners, brotherhoods, and the urban commune of Tongeren. The elaborate Rayonnant Gothic architecture of the eastern part of the church bears witness to the prestige associated with the church’s chapter, which claimed an episcopal past.