This paper examines the role of Swedish engineering firms in Iran’s architectural modernization during the First Pahlavi era, foregrounding infrastructure as a critical yet underexplored instrument of state formation, national integration, and geopolitical self-assertion. While the contributions of prominent European engineering firms to Pahlavi modernization have long been recognized, the role of Scandinavian companies has received little scholarly attention. Addressing this lacuna, the study investigates the technical, conceptual, and cultural dimensions of Swedish engagement in Iran, with particular reference to the Ahvaz White Bridge and the Ghazian–Mian Poshteh Bridge. Adopting a descriptive–analytical methodology and drawing on archival materials, historical documentation, architectural records, and field investigations, the research traces how Scandinavians facilitated the transfer of modernist ideas, reconfigured spatial orders, and reshaped Iran’s building culture. The findings suggest that Swedish firms performed a role far exceeding that of contractors or technical service providers. Their projects introduced advanced materials, including reinforced concrete and steel, together with movable bridge technologies previously unknown in Iran, while simultaneously embodying the broader discourse of Pahlavi modernisation. These structures emerged not only as feats of engineering, but also as visible symbols of state authority and of Iran’s aspiration to reposition itself within global modernity. Their deliberate siting in strategically sensitive regions further underscores their geopolitical significance and their function as instruments of territorial integration. Beyond their technical contribution, Swedish companies acted as cultural agents and conduits for international architectural models, participating in a form of “architectural diplomacy” that facilitated the social reception of new architectural vocabularies, and thereby helped legitimise modernist aesthetics. By bringing these issues into focus, this study contributes to scholarship on transnational architectural history, technology transfer, and the geopolitics of infrastructure. It demonstrates how peripheral European actors shaped non-Western trajectories of modernisation and how the built environment was instrumentalised in state-building projects.