A Frankish kingdom established by the Montferrat dynasty after the Fourth Crusade (1202-1204) in Macedonia, with its capital at Thessalonica (mod. Thessaloniki, Greece), which survived for only two decades until it was overrun by the Greeks of Epiros in 1224.
The creation of a separate kingdom around Thessalonica, the second city of the Byzantine Empire, was not envisaged in the pact of 1204 by which the crusaders at Constantinople made arrangements for the future governance of their conquests on Byzantine territory. According to the chronicler Geoffrey of Villehardouin, the unsuccessful candidate in the election of a Latin emperor was to receive “all the land across the strait toward Turkey and also the Isle of Greece” [Villehardouin, La Conquête de Constantinople, ed. Edmond Faral, 2d ed., 2 vols. (Paris: Les Belles Lettres,1961), 2:64]. The election of Baldwin of Flanders as emperor meant that Boniface of Montferrat should have received these lands; however, Boniface persuaded both Baldwin and the Venetians to exchange “the land . . . toward Turkey” (that is, Byzantine Anatolia) for Thessalonica and its environs, thus ensuring a contiguous block of territory. Boniface continued to call himself marquis and was never crowned king of Thessalonica, although he was well placed to capitalize upon his possessions: he had occupied the city, conquered territories as far as Thessaly and central Greece, and married Maria (Margaret) of Hungary, widow of the Byzantine emperor Isaac II Angelos.
Relations between Boniface and Emperor Baldwin were at first strained. However, the threat posed to both Constantinople and Thessalonica by the Bulgaro-Vlach coalition under Kalojan (Johannitsa), as well as Baldwin’s death at their hands in late 1205, made reconciliation both urgent and possible. The new emperor, Henry, married Boniface’s daughter Agnes, and Boniface paid homage to him. In September 1207 Boniface was killed in battle by the Bulgarians, leaving an infant son, Demetrius, under the regency of his widow Margaret and a council of Lombard lords. The latter sought to replace Demetrius with his older half-brother William VI, marquis of Montferrat. However, Emperor Henry moved on Thessalonica in December 1208 and secured the coronation of Demetrius as the first (and, as it happened, last) ruling king of Thessalonica (9 January 1209). Henry’s actions were endorsed by Pope Innocent III, who recognized Demetrius as king in March 1209 and took him under papal protection.
The emperor and his brother Eustace busied themselves with occupying the Maritsa Valley and securing control of the Via Egnatia around Thessalonica, but in the summer of 1210 the Epirot Greeks attacked the kingdom. Although Henry responded swiftly and saved the city, land was lost in Thessaly and the capital effectively cut off from the rest of the kingdom in Greece. The death of Henry in 1216, and the failure of his successor, Peter of Courtenay, to open up a route to Thessalonica from Durazzo (mod. Durrës, Albania), left the kingdom struggling for its existence. In 1221 the loss of Serres and Platamonas meant that there was no safe land route between Thessalonica and Constantinople, and in December 1224 the city surrendered to the Epirot Greeks. A crusade mounted by William VI of Montferrat failed to achieve anything, and Demetrius was forced to flee to Italy. The kingdom of Thessalonica was effectively at an end.
Frankish claims to Thessalonica persisted through the thirteenth century. Demetrius passed his claim to Frederick II, the Holy Roman Emperor, and in 1266 the exiled Latin Emperor of Constantinople, Baldwin II, granted title to the kingdom to Hugh IV of Burgundy. The Montferrat claim to the city ended with the marriage of Yolande of Monferrat to Andronikos II Palaiologos in 1284; a later Burgundian claim was heard of no more after it was sold to Philip of Taranto in 1331.