Embolus

Embolus a covered portico or cloister; in ecclesiastical language a cloister surrounding the external walls of a church, serving as an ambulatory in hot, rainy, and dirty weather, and also affording a convenient passage for the priests and ministers of the church from the bema and diaconicum to the narthex. These porticos were generally vaulted, and highly ornamented with mosaic pictures. Such porticos were found at St. Sophia, Constantinople; St. Michael, at Anaplus; and the Deipara, at Jerusalen.