Despite its status as one of Istanbul’s most iconic monuments, the Sultan Ahmed Mosque (1609–17) met with considerable opposition when embarked upon by its founder, the Ottoman sultan Ahmed I, who had won no holy wars to fund or justify the project. Ahmed sought to legitimate his mosque through a series of festive events held during and after its construction and designed to propel it into the public consciousness. This article examines the most lavish of these events—a ceremony held for the closing of the mosque’s dome—in light of a hitherto unnoted manuscript describing the occasion. Staged shortly before the official opening of the mosque, the ceremony was unconstrained by the protocol of an inauguration proper and brought together a unique set of symbolic features to proclaim the monument’s legitimacy. Besides the charged act of capping the dome, the ceremony included a royal encampment in the mosque’s courtyard—a military allusion that cast Ahmed as a victor—and was attended by foreign ambassadors, who stood for the sultan’s vanquished enemies. This extravaganza boosted Ahmed’s successful campaign to vindicate his mosque and, though unparalleled in its particulars, provides a revealing case study of how the Ottomans used ceremonial to reinforce the semantic purport of their architecture.