The history of Almyros begins with the ancient city of
Halos (about 10 km [6.2 mi] south of Almyros), the ruins of which can still be visited. Halos was a very important and populous town, famous for its port and for its role in the
Persian Wars. After the
Byzantine Empire, because of pirate raids, they built the town in the place that it is today. Ancient Halos was still mentioned in the works of
Stephanus of Byzantium (6th century). The medieval successor settlement of Halmyros is first mentioned in the 11th century, when it was listed as a Christian diocese. During the Middle Ages, sources refer to "two Halmyroi" (
δύο Άλμυροι): one of these was at the same site as ancient Halos, 6 km southeast of the present-day town of Almyros, while the other was an associated port on the Pagasitic Gulf. At the old acropolis of Halos, the remains of a couple of stone towers (one at the highest point of the acropolis, the other at the base, overlooking the modern motorway) attest to the site's continued existence in the Middle Ages. The lower town of Halmyros existed between two fortresses, one at the mouth of the Platanorrema and the other at the site of present-day Tsengeli (which is now inaccessible due to being the site of an airport). Almost nothing remains of either fortress. Remains of the old city walls have been found in the area between the two fortresses. In 1158, Halmyros was attacked and plundered by a naval force commanded by
William I of Sicily. The Pisan church of St. Jacob was burned down in the attack. Halmyros's Venetian community was hit badly by
the arrest of all Venetians living in Byzantine territory in 1171. In 1198, the "two Halmyroi" were mentioned for the first time, in a document under
Alexios III Angelos granting special privileges to the Venetians. In the 1204
Partitio terrarum imperii Romaniae after the
sack of Constantinople, the "duo Almiri" are mentioned among the Thessalian possessions of Alexios's wife,
Euphrosyne Doukaina Kamatera. Halmyros was then assigned by
Boniface of Montferrat as the place where the former Alexios III would reside as a private citizen. Later, Halmyros became a property of
William of Larissa and later still was assigned to
Margaret of Hungary, Boniface of Montferrat's widow. ==Municipality==