until the 7th-century arab islamic conquests, syriac christianity was thus divided between two empires, sassanid persia in the east and rome/byzantium in the west. the western group in "syria" (ancient aramea), the eastern in parthian, persian and (for merely two years) roman assyria, east of the tigris and so of mesopotamia. syriac christianity was divided from the 5th century over questions of christological dogma, viz. nestorianism in the east and monophysitism and dyophysitism in the west.