'arx' originates from Latin, specifically the word 'arx' (genitive 'arcis'), where the root meant 'citadel' or 'high fortified place'.

'arx' was used in Classical Latin to denote a fortress on a height; it passed into Late Latin and Medieval Latin usage and has been borrowed into English in scholarly or literary contexts as 'arx'.

Initially, it meant 'a fortified height or citadel' in Latin, and in English it has retained that primary meaning while also acquiring a figurative sense of 'stronghold' or 'center of power'.