Thessaly is a central Greece south of Macedonia and separated from Epirus by the Pindos Mountains. It is characterized by a large central plain formed by the Peneios River and surrounded on all sides by high mountains. The main city was always Larissa, other important centers being Trikala and Stagoi (modern Kalabaka) in the west, Lamia and Neopatras (modern Ypati) in the south, and Demetrias and Nea Anchialos on the sea to the east. The major north-south road ran from Thermopylai north to Larissa, continuing to Macedonia, either through Servia or along the coast to Thessaloniki; the main east-west road ran to Trikkala and thence either north to Kastoria or west to the pass of Porta, or, in the summer months, over the pass of Metsovo. In late antiquity the province of Thessaly possessed 16 cities, including the islands of Skiathos, Skopelos, and Peparisthos. In the 6th-8th centuries Slavs settled in the north and north-west, and Vlachs were established in large numbers by the 11th century, forming a separate administrative subdivision, the Megale Vlachia.
According to Abramea, five Thessalian cities disappeared from the sources after the 7th century, seven (including Larissa, Trikkala, and Demetrias) continued to exist, and at least nine were built from the 9th century onward (including Halmyros and Stagoi). In fact, however, the continuity of urban life in Thessaly is less evident. In the 12th century trade seems to have been important in Thessaly, and the Treaty of 1198 gave the Venetians trading privileges in many places. There were Jewish communities at Gardiki, Halmyros, Lamia, and Besaina. The area was subjected to hostile invasions; esp. serious were those of the Bulgarians in the 10th century and the Normans in 1082.
After 1204 the Latins controlled the eastern cities while the west seems to have been independent. The area was contested by the Epirots and Nicaeans, but John I Doukas (1267?-1289?),assuming the title sebasiokrator, established an independent principality in Thessaly with a capital in Neopatras; he expanded his territory to the east, thus becoming involved in conflict with Michael VIII; with the help of Charles I of Anjou and the Latin dukes of Athens he managed to repel Byzantine attacks. John II (1303-1318) was also Western-oriented and sought the support of the Venetians, who were importing agricultural produce from Thessaly. The invasion of the Catalan Grand Company in 1309 was detrimental for Thessaly; after John II's death the Company occupied the south of the country, including Neopatras and Lamia. Stephen Gabrielopoulos preserved the independence of Thessaly until 1332/3, but thereafter it fell to John II Orsini of Epirus and in 1335 to Constantinople. Large landholding developed in Thessaly, acquiring a semifeudal character, and Thessalian seigneurs supported John VI Kantakouzenos in his struggle for power. It has been hypothesized that these feudal forces allowed Thessaly to resist the attacks of Stefan Urog IV Dugan. In 1348, however, the Thessalian seigneurs acknowledged Serbian sovereignty while retaining their traditional privileges. After Dugan's death Thessaly formed the center of the domain of the "emperor" Symeon Urog ; this Serbian ruler encouraged the (at least external) Hellenization of the country. When his son and heir John Urog retired to a monastery in 1373, power was seized by the caesar Alexios Angelos Philanthropenos, who governed Thessaly as a vassal of John V. In 1393 the Ottomans conquered Thessaly.
In ecclesiastical terminology the name Thessalia and derivations were applied (especially in the 12th century) to Thessaloniki, and its metropolitans were called "of the Thessalians" (e.g., Laurent, Corpus 5.1, nos. 459, 461). Byzantine fortifications can be found at several places in Thessaly (including Trikkala, Larissa, and Lamia), and there are important churches at Porta Panagia (founded in 1283 by John I Doukas) and Stagoi; Nea Anchialos and Demetrias preserve the ruins of many Early Christian buildings, while the monasteries at Meteroa and the ruined, largely 14th-century city at Phanarion are especially noteworthy. Architecturally, the churches of Thessaly were influenced by currents from Macedonia, although in the 13th-14th centuries there were also borrowings from Epirus.
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