This paper argues that the early Republican attempts to reintegrate the Ottoman past into nationalist narratives later found their reflections in discussions regarding the preservation of İstanbul’s diverse heritage, coinciding with the redefinition of Turkish nationalism in the 1940s, incorporating Islam and marking a departure from the foundation ideology of the Republic of Turkey. In 1939, the Republican authorities decided to celebrate the 500th anniversary of the Ottoman conquest of Constantinople in 1953. The Commission for the Preservation of Antiquities (Muhafaza-ı Asar-ı Atika Encümeni)—the body responsible for the preservation of historic monuments in İstanbul—was tasked with conducting restoration and repair works for the celebrations. Although the celebrations did not receive much attention in the following years, the annual celebrations in the city have now become a significant aspect of present-day İstanbul, which glorify its Ottoman-Islamic past. By presenting its negotiations and contestations with other state actors in the context of these preparations, this paper explores the role of the Preservation Commission in appropriating the inherited remnants of İstanbul’s multifaceted past as “national monuments.”