The morphology of Iranian historical cities often developed organically over centuries. However, during the Safavid era, urban design was guided by predetermined geometric principles, especially in capital cities such as Qazvin and Isfahan. Central squares, monumental gardens, and axial streets were conceived as structuring elements that organized surrounding functions in a highly regulated manner. This research investigates the Saadat Abad complex of Qazvin, the first Safavid capital, to uncover the role of spatial geometry in shaping its royal ensemble. Through a historical-analytical approach, supported by comparative case studies, textual sources, travelers’ accounts, and surviving cartographic evidence, the study demonstrates that the royal square (Maidan-e Saadat Abad) possessed the highest geometric priority. Surrounding elements such as mosques, gardens, bazaars, and caravanserais were required to adapt through transitional spaces, reorientation, or hierarchical adjustments in order to preserve the square’s orthogonal geometry. The findings reveal a consistent application of rectilinear planning, hierarchical geometric order, and modular structuring across Safavid capitals, reflecting the political symbolism of geometry as well as its functional role in urban organization.