_Prothesis and Diakonikon._--Two chapels that in Byzantine churches almost invariably occur right and left of the bema with which they communicate directly are usually called the prothesis and diakonikon; they were sacristies, used respectively for the preparation of the mass and as a treasury or vestry. Du Cange in both editions placed them in the two exedras of the eastern hemicycle, and in this he is followed by Salzenberg. The impossibility of this arrangement is shown by Neale, who suggests that two chambers on either side of the bema which Du Cange thought were only supplementary were the sacristies in question. The chapels at the east end of S. Sophia have now been built up, but the doors that led into them still exist. We are not however certain that these chapels were built with the church. Paulus does not mention them, and there do not appear to have been chapels in this position at S. Sergius. In regard to the use of the prothesis and diakonikon, Dr. Freshfield[126] considers that the procession with the bread and wine called the _Megale Eisodos_, described in our last chapter, only became a part of the ritual in the reign of the successor of Justinian, to whose time the Cherubic Hymn sung during the ceremony is referred. The earlier liturgies, he says, contain no directions for this ceremony, but merely speak of the deacon as moving the elements from the prothesis table to the altar, and he concludes that the two side-chapels found in so many churches belong to a time subsequent to Justin II. Two narrow passages however, right and left of the bema, at S. Sophia, S. Sergius, S. Irene, and S. Vitale seem to show that they were intended for access to lateral portions used in connection with the bema, even if these parts were merely screened from the aisles, and a comparison of many early churches in Syria and Asia Minor proves that such chapels were in frequent use if not essential long before Justinian built his church.[127] See our figures 31 and 32, and compare Cattaneo, page 60.