It was on Christmas Eve of the year 820 in the Church of Hagia Sophia in Constantinople that Emperor Leo V was replaced by one his trusted generals, Michael II, because Mike had Leo murdered.
Leo had been Emperor-ing for seven years, and accomplished some notable administrative advancements, including forcing Bulgaria into a peace agreement and persecuting (i.e. murdering and confiscating the land and property of ) a denomination called Paulicians who were not quite Catholic enough.
When Leo jailed Michael for suspicion of conspiracy, the latter organized the assassination of the Emperor in the palace chapel on Christmas Eve, 820. Leo was attending the matins service when a group of assassins disguised as monks suddenly threw off their robes and drew their weapons. In the dim light they mistook the officiating priest for the Emperor and the confusion allowed Leo to snatch a heavy cross from the altar and defend himself. He called for his guards, but the conspirators had barred the doors and within a few moments a sword stroke had severed his arm, and he fell before the communion-table, where his body was hewed in pieces. His remains were dumped unceremoniously in the snow and the assassins hurried to the dungeons to free Michael II. Unfortunately for them Leo had hidden the key on his person, and since it was too early in the morning to find a blacksmith Michael was hastily crowned as emperor with the iron clasps still around his legs. Leo's family (including his mother and his wife, Theodosia) was exiled to monasteries in the Princes' Islands. His four sons (including ex co-emperor Symbatios) were castrated, a procedure so brutally carried out that one of them died during the "operation".