(1204-1224), within the
Latin Empire of Constantinople Demetrius was the son of Marquis
Boniface of Montferrat by
Margaret of Hungary, the widow of
Byzantine Emperor Isaac II Angelos (d. 1204). In the aftermath of the
Fourth Crusade, Boniface had secured for himself the region of
Macedonia in the division of the spoils, creating there the
Kingdom of Thessalonica. Marrying the former Byzantine empress, he found it easier to attract support from the members of the Byzantine aristocracy. When Boniface's son was born in Thessalonica in 1205, he was named after
Saint Demetrius, the patron saint of Thessalonica. Boniface was killed in a battle against the
Bulgarians in 1207, and
Kaloyan of Bulgaria promptly besieged Thessalonica. The siege ended with Kaloyan's murder, but Demetrius' rule was not secure. Since he was a child, regency was held by his mother Margaret. Some of the most influential magnates of the kingdom conspired against the regency, plotting to replace the infant ruler with his half-brother, Marquis
William VI of Montferrat. The
Latin Emperor Henry of Flanders determined to stem this movement and advanced on Thessalonica in December 1208. The barons, led by Count
Umberto II of Biandrate, shut the gates of the city before the emperor and issued several unreasonable demands. The emperor pretended to accept Biandrate's terms (provided that Margaret accepted them) long enough to gain entrance into the city. Margaret was then instructed to overrule the terms and Henry crowned young Demetrius king on January 6, 1209, extracting oaths of homage from the Lombard barons. The emperor's actions were confirmed by
Pope Innocent III. The rights of the young king were still threatened by Biandrate's Lombard garrisons of important fortresses like
Serres and
Kavala. Henry took Serres but Kavala held out. Hoping to reach a reconciliation, the emperor summoned the nobility of the Kingdom of Thessalonica to a
parliament at Ravennika, but many lords did not submit. After further military action, Henry obtained the submission of Biandrate and the remaining Lombard lords. He defeated the
Epirote attack on Thessalonica in 1210 and left his younger brother Eustace as regent for King Demetrius. The situation changed again on Henry's death in 1216. The new Latin Emperor,
Peter of Courtenay, was won over by the Lombard lords and invested William of Montferrat with the kingdom before leaving
Italy. The Queen Mother Margaret and her son
John Angelos (maternal half-brother of Demetrius), fled to
Hungary, but Demetrius apparently remained in place, while the Emperor Peter was captured and eventually executed by
Theodore Komnenos Doukas in Epirus. Doukas exploited the dissension among the nobility in Thessalonica to gradually conquer the kingdom's fortified towns one after another. Although William of Montferrat proved unwilling to dispossess his half-brother, he agreed to lead a crusade to the relief of Thessalonica in 1222, and prepared to set out, sending ahead Umberto of Biandrate. Before the main force of this crusade reached Thessalonica, however, Theodore forced the surrender of the city in December 1224. Together with the Latin archbishop, King Demetrius fled to the court of Emperor
Frederick II in Italy. He participated in Frederick's crusade to the
Levant, and died in 1230 at
Amalfi, after ceding his rights to Thessalonica to Frederick II. Demetrius was married to Hermingarde, from the
La Roche family that ruled the
Duchy of Athens. Some earlier researchers assumed that Demetrius had children, or even grandchildren, but later scholars have shown that those presumed descendants were related to Demetrius in different ways, thus being just cousins. ==References==