in all ancient cities, was a fortified eminence or rock, either within or close by the city itself. The arx at Rome was a part of the Capitoline Hill, the other part containing the Capitoline temple. In Greek towns the arx was called ἄρξα or ἄρξωρας, and in several of them it bore a distinct name; whence at Thebes it was called the Cadmea, at Argos Larissa, at Corinth Acrocorinthus, and at Athens, sometimes Cecropia, or simply ἄρξας. The modern name citadel does not correspond with the term arx in every respect, the latter being always situated on an eminence. (L-S.)