The Battle of Demetrias was a sea engagement fought at Volos in Greece in the early 1270s between a Byzantine fleet and the assembled forces of the Latin barons of Euboea (Negroponte) and Crete.

Following the recapture of Constantinople and the restoration of the Byzantine Empire in 1261, one of the chief priorities of Emperor Michael VIII Palaiologos (r. 1259–1282) was the defence of his capital from a Venetian attack.

[4] In the early 1270s (the exact date is uncertain, most recent scholars favour 1272/3 or 1274/5),[a] Michael VIII Palaiologos launched a major campaign against John I Doukas, ruler of Thessaly.

The joint Latin fleet, composed of Lombard and Venetian vessels from Negroponte and Venetian-held Crete, is variously given at 30 (Gregoras) to 62 (Sanudo) ships.

[8] His arrival boosted the Byzantines' morale, and Palaiologos's men, ferried on board the ships by small boats, began to replenish their casualties and turn the tide.

In Euboea, Licario's major gain and personal fief, the Byzantine forts were gradually retaken by the Lombards, until they recovered the entire island by 1296.

Some historians (Deno J. Geanakoplos,[11] Jean Longnon [fr],[12] Donald Nicol) followed the date 1275 proposed in the 19th century by Hopf interpreting the chronicle of Marino Sanudo, and placed the Thessalian campaign after the Council of Lyon.

[13] Others adopted the date 1271 proposed by the 17th-century Jesuit scholar Pierre Poussines interpreting the chronicle of G. Pachymeres, a datation reactualized by Raymond-Joseph Loenertz in the 1960s.