In October 1906, an Egyptian-Ottoman boundary commission delimited a “separating administrative line” between the Sinai Peninsula and the Ottoman Empire. This paper explores the perspectives of the Egyptian state and Egyptian nationalists on the border’s formation and the Sinai’s transformation into a geographic site of politics—its territorialization. The boundary represented the diplomatic solution to Ottoman, British, and Egyptian tensions that had animated the Taba/Aqaba crisis earlier that year. The existing scholarship on this topic focuses on British diplomatic considerations and, to a lesser extent, Ottoman calculations. This paper highlights the Egyptian role in the peninsula’s territorialization by examining the positions taken up by nationalist writers in Egyptian newspapers, state rationales offered in written accounts by members of the Egyptian boundary delegation, and published archival material from the British Foreign Office detailing both internal deliberations and cooperation with Khedive Abbas Hilmi II. This paper argues that Abbas Hilmi II had reasons independent of British interests to support a boundary running from Rafah to the head of the Gulf of Aqaba and thus formalize the entirety of the Sinai Peninsula into Egypt. This contradicts the established narrative that Egyptians played a passive role in the formation of their modern borders. Instead, Abbas Hilmi II saw an opportunity to reaffirm his autonomy before the Ottoman sultan who threatened to upset the Cairo-Constantinople imperial relationship by asserting his direct authority over the Sinai Peninsula and challenging the British. The Egyptian state also sought to finalize a contentious process of shifting boundary conceptions in the peninsula in its favor, an ongoing process since Muhammad Ali Pasha was awarded dynastic rule over Egypt in 1841. Egyptian nationalists, however, derided what they saw as their state’s acquiescence to British demands, arguing instead for the validity of the sultan’s claims. They criticized British encroachment on Ottoman lands and sovereignty, and they found little value in Sinai for Egypt. This disconnect demonstrates the struggle between the Egyptian state and the wider public over the construction of a common conception of an emerging Egyptian territoriality. On a final and more theoretical note, this paper also argues that the history of this boundary demonstrates how geography increasingly became a site of politics through the development of cartographic and centralized administrative practices, how sovereignty and political authority became increasingly associated with territory, and how modern diplomacy was fundamental to these developments.