Urban expansion is currently a major trend in capital cities throughout the developing world. This trend is playing a major role in changing the historical fabric and contexts of those cities. Predictably, the built heritage of Old Muscat is also being affected by urban expansion and development. This paper investigates the nature of the relationship between preservation of cultural heritage and urban expansion through a study of the way the defence sites of Muscat - the capital city of Oman- are managed. The paper investigates the points of collaboration and conflict between cultural heritage and urban expansion in Old Muscat, and looks at how a balance may possibly be maintained between them. The paper shows that various types of defence sites such as forts, castles, towers, walls, and gates represent an important part of the identity and history of the place. It also shows that although the defence sites of Old Muscat have received a relatively large amount of attention from urban planners, the management and utilization of these sites is questionable. It also shows that the modernization of the city, and the associated phenomenon of urban primacy, have both led to a cultural shift that is affecting people's perception of the defence sites.