CIE´RIUM(Κιέριον: Eth. Κιεριεύς), a town in Thessaly, which is identified by Stephanus B. with Arne (Steph. B. s. v. Ἅρνη), the chief town of the Aeolian Boeotians in Thessaly, from which they emigrated to Boeotia. The site of Cierium was first discovered by Leake, who from inscriptions and coins found on the spot has proved that it stood at the modern village of Mataránga, between the Enipeus or Apidanus, and a tributary of that river. The territory of Cierium adjoined that of Metropolis; and we learn from an inscription cited by Leake that the adjustment of their boundaries was a frequent subject of discussion between the two people. The identification of Arne and Cierium is confirmed by an inscription, which mentions Poseidon Cuerius (Κουέριος), a name evidently connected with the river Cuarius or Coralius in Boeotia. (Strab. 9. p. 411.) The expelled Boeotians gave this name to the river, and founded upon its banks a temple of Athena Itonia in memory of their former abode in Thessaly. We may therefore conclude that the river upon which Cierium stood was called Cuerius, Cuarius or Curalius, more especially as Strabo (9. p. 438) mentions a river Curalius in Thessaly, flowing through the territory of Pharcadon in Histiaeotis past the temple of Athena Itonia into the Peneius; in which the only inaccuracy appears to be that he makes it flow directly into the Peneius. Pausanias (Paus. 1.13.2) also appears to speak of this temple of Athena Itonia, since he describes it as situated between Pherae and Larissa, which is sufficient to indicate the site of Cierium. Leake supposes with much probability that the name of Arne may have been disused by the Thessalian conquerors because it was of Boeotian origin, and that the new appellation may have been taken from the neighbouring river, since it was not an uncommon custom to derive the name of a town from the river upon which it stood.
Cierium is not mentioned under this name in history; but it occurs under the form Pierium, which is undoubtedly only another appellation of the same place, πand κbeing, as is well known, often interchangeable. Pierium was probably the general, and Cierium the local form. Pierium is first mentioned by Thucydides (Thuc. 5.13). It is called Piera and Pieria by Livy (Liv. 32.15, 36.14), in both of which passages it is mentioned in connection with Metropolis. In the Armenian translation of Eusebius we find the name of Amyntas the Pierian in the list of the Strategi who governed Thessaly after the battle of Cynoscephalae. Aelian ( N. An. 3.37) speaks of Pierus in Thessaly. (Leake, Transactions of Royal Society of Literature, vol. i., Northern Greece, vol. 4. p. 498, seq.; Müller, Dorians, vol. 2. p. 476.)