The Constantinople massacre of 1821 was orchestrated by the authorities of the Ottoman Empire against the Greek community of Constantinople (modern Istanbul) in retaliation for the outbreak of the Greek War of Independence (1821–1830). As soon as the first news of the Greek uprising reached the Ottoman capital, there occurred mass executions, pogrom-type attacks, destruction of churches, and looting of the properties of the city's Greek population. The events culminated with the hanging of the Ecumenical Patriarch, Gregory V and the beheading of the Grand Dragoman, Konstantinos Mourouzis.
In early March 1821, Alexandros Ypsilantis crossed the Prut river and marched into Moldavia, an event that marked the beginning of the Greek War of Independence. Immediately in response of rumors that Turkish citizens had been massacred by Greeks in the Danubian Principalities, particularly in Iași and Galați, the Grand Vizier ordered the arrest of seven Greek bishops in Constantinople. In addition, on the evening of April 2, the first news of the Greek Revolt in southern Greece reached Constantinople.
Leading personalities of the Greek community, in particular the Ecumenical Patriarch, Gregory V, and the Grand Dragoman, Konstantinos Mourouzis, were accused of having knowledge of the revolt by the Sultan, Mahmud II, but both pleaded innocence. Nevertheless, the Sultan requested a fatwa allowing a general massacre against all Greeks living in the Empire from the Shaykh al-Islām, Haci Halil Efendi. The Shaykh obliged, however the Patriarch managed to convince him that only a few Greeks were involved in the uprising, and the Shaykh recalled the fatwa. Haci Halil Efendi was later exiled and executed by the Sultan for this.