Construction site management in minor historical centers is particularly challenging due to limited accessibility, the fragility of the built heritage, and the strong impacts on local communities, affecting logistics, safety, and coordination of activities. In these contexts, informational and regulatory complexity, especially related to safety compliance, is amplified by the dynamic interactions between the construction site and the urban environment. Despite the increasing adoption of digital technologies such as Building Information Modeling (BIM), Internet of Things (IoT), and Digital Twins (DTs), construction site management often remains fragmented and reliant on heterogeneous data, leading to potential inefficiencies and decision-making risks. This study proposes a multi-level ontological framework to support the integrated management of construction sites in fragile urban contexts, with a particular focus on safety. The framework enables the coherent integration of physical, operational, regulatory, and contextual information, providing a shared semantic foundation for interoperability with BIM and DTs systems. The explicit structuring of heterogeneous knowledge promotes more informed decision-making, context-aware and efficient site management, and the optimization of operational flows in complex urban settings.