Datianus is mentioned in Gruter's Inscriptions as having determined the limits between the territories of Pax Julia and those of Ebora, both cities in the southern part of Lusitania. If we recollect the neighbourhood of those places to Cape St. Vincent, we may suspect that the celebrated deacon and martyr of that name has been inaccurately assigned by Prudentius, etc., to Saragossa or Valentia. See the pompous history of his sufferings, in the Memoires de Tillemont, tom. v. part ii. p. 58-85. Some critics are of opinion that the department of Constantius, as Caesar, did not include Spain, which still continued under the immediate jurisdiction of Maximian.