The important mosaics in the north inner aisle of the Church of S. Demetrios were largely destroyed in the fire of 1917. They had been unrecorded until ten years previously when their covering of Turkish plaster was removed.
On 1 August 1907, the Turkish authorities set under way major repairs of the Casimir Çamii (Κασιμιὲ Τʒαμισί) in Thessaloniki, at that time a somewhat dilapidated building which had been last renovated in 1841. Operations were completed by June 1908. The name of the mosque did not conceal its original dedication as the Byzantine church of S. Demetrios, which had been one of the most famous centres of pilgrimage for Orthodox Christians until its Muslim conversion in 1492–3. In the course of these repairs occurred the unexpected discovery of surviving Christian mosaics and wall-paintings under a coating of plaster. The first mosaics were revealed in December 1907, and comprised three bust figures within medallions, situated in the central part of the north inner aisle (Plates 1a, 15a). The discovery was greeted with excitement by P. N. Papageorgiou, who took photographs which he communicated to the Turkish Nomarch and the Oecumenical Patriarch. The news was published in ecclesiastical news-sheets in Thessaloniki (December 1907) and Istanbul (26 January 1908). Meanwhile further soundings and discoveries continued in the mosque.