Emperor Leo V the Armenian instituted a second period of Iconoclasm in 815, again possibly motivated by military failures seen as indicators of divine displeasure, and a desire to replicate the military success of Constantine V. The Byzantines had suffered a series of humiliating defeats at the hands of the Bulgarian Khan Krum, in the course of which emperor Nikephoros I had been killed in battle and emperor Michael I Rangabe had been forced to abdicate. In June 813, a month before the coronation of Leo V, a group of soldiers broke into the imperial mausoleum in the Church of the Holy Apostles, opened the sarcophagus of Constantine V, and implored him to return and save the empire.