Demetrias (Ancient Greek: Δημητριάς) was an ancient Greek city in Magnesia (east central Greece), near the modern city of Volos. It was founded by Demetrius Poliorcetes, and became the favourite residence of the kings of Macedon.
In 196 B.C., the Romans, victorious in the battle of Cynoscephalae over Philip V of Macedon in the previous year, took possession of Demetrias, but four years later the Aetolian League captured it by surprise. The Aetolians allied themselves with Antiochus III of the Seleucid Empire in the Roman–Syrian War. This ended in the defeat of Antiochus. The Romans then returned Demetrias to Philip, who had been their ally in this war. It remained a Macedonian possession until the battle of Pydna in 169 B.C.
According to Procopius (De Aedificiis, 4.3.5), Demetrias was rebuilt by Justinian I (r. 527–565), but other evidence points to the possibility that "ancient urban life may have already come to an end by the beginning of the 6th century" (T.E. Gregory). Its territory was settled by the Slavic tribe of the Belegezitai in the 7th/8th centuries, raided and sacked by the Saracens in 901/2, and by rebels during the Uprising of Peter Delyan in 1040.
Following the Fourth Crusade, the town was granted to the exiled Byzantine empress Euphrosyne Doukaina Kamatera, and after her death in 1210 to Margaret of Hungary, the widow of the King of Thessalonica, Boniface of Montferrat. The city came under the rule of Manuel Komnenos Doukas ca. 1240, but was de facto controlled by a branch of the Melissenos family. In the 1270s, the Byzantines scored an important victory against the Venetians and the Lombard barons of Euboea at Demetrias.
The Catalan Company sacked the town in 1310 and kept it until 1381 at least, but from 1333 on, it began to be abandoned for neighbouring Volos. It was finally captured by the Ottoman Empire in 1393.
- William Smith, Dictionary of Greek and Roman Geography (1854), entry "Demetrias"
- Annuario Pontificio 2013 (Libreria Editrice Vaticana 2013 ISBN 978-88-209-9070-1), "Sedi titolari", p. 880
- Gregory, Timothy E. (1991). "Demetrias". In Kazhdan, Alexander. The Oxford Dictionary of Byzantium. Oxford and New York: Oxford University Press. pp. 603–604. ISBN 978-0-19-504652-6.