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William VI of Montferrat

William VI (c. 1173 – 17 September 1226) was the Marquess of Montferrat from 1203 and pretender to the Kingdom of Thessalonica from 1207.


Boniface I's eldest son, and his only son by his first wife, Helena del Bosco, William stood originally to inherit all his father's possessions. He participated in diverse campaigns with his father, including the Battle of Montiglio, in which the men of Asti were defeated in 1191. Between 1193 and 1199, he appeared in many of his father's public acts. On 12 June 1199, he was put in charge of Acqui Terme with twenty knights to combat the Alessandrini, and, on 27 October, he was present near Saluggia for the signing of a pact with the commune of Vercelli.

War with Asti

Boniface I joined the Fourth Crusade as a Christian leader in 1203. In accordance with promises made to Asti and Alessandria, he officially abdicated the marquisate to William before he left. Immediately, William turned towards Asti, then protected by Milan. The Astigiani had a history of rebellion and were growing in power. In August, with his father beside him, he formed an alliance with Alba and Alessandria, another rebellious commune, against Asti. His allies proved of little worth as he had to make many concessions to them and was still defeated in the field. In April 1206, he opened negotiations with Asti. The peace treaty was embarrassing for Montferrat, but it was accepted by all three allies. William promised to get his father's ratification, but his father died on Crusade unaware of any peace back home.

War against the Ghibellines

Traditionally, the Aleramici adhered to the Ghibelline faction, which supported the Hohenstaufen and their Italian schemes. William, however, lent his support to Otto of Brunswick, the Guelph claimant to the imperial title. Though William expected to see the power of an emperor levelled against his foes, the only aid he received from Otto was directed against small local potentates which posed little real threat. The only great success of the alliance was the sack of Cuneo.

Relationship with Frederick II

At the Diet of Lodi, William abandoned Otto finally in favour of Frederick II, the Hohenstaufen claimant. On 15 July 1212, he was in Genoa with the other Ghibelline lords to receive Frederick. William led the young emperor from the city to the road which led to Germany. In 1215, William participated in the Second Lateran Council, there arguing the cause of Frederick against Otto. He travelled many subsequent times into Germany to speak to Frederick and during these absences, his enemies plotted against him. In their attempts to seize his lands, however, they were largely unsuccessful.

During his times in Italy, William remained at war with Asti and Alessandria, but without result.

Claims in Greece

During the exhausting years battling rebels and Guelphs, William resolved to travel to Greece to defend the conquests of his father, which had been formed into the Kingdom of Thessalonica. To this end he was urged by the churchmen of his realm and also by the troubadour Elias Cairel. When he finally decided to take the cross, aware of the insignificance of his contribution to the total effort, he decided to head by way of Egypt, at the suggestion of Pope Honorius III. But the arrival of his half-brother Demetrius, fleeing the onslaught of the Greeks and the conspiracy of the Lombards, led by their kinsman Oberto II of Biandrate, who desired to make William king as his father's successor, convinced him to go to Greece.

Several times he prepared to head out, but each time was detained by the threats of his enemies in Piedmont or by economic restraints which compelled him to mortgage his marquisate to Frederick II. Finally, he cowed some cities into giving him aid in men. Nevertheless, he was present at Capua, Ferentino, and Sora with Frederick II in February 1223. Delayed again and again, he drank a toast at Brindisi to his setting off in 1225, but he fell ill at the last minute. His fleet remained in port until Spring 1226, when, under urging from Honorius, it finally cast off. The delays had been fatal and William himself died at Almyros on 17 September. The rest of his army was hit by a dysentery epidemic and melted away.

Marriages and children

During his infancy, William was betrothed to Sophie, daughter of Frederick I, Holy Roman Emperor. The marriage took place in 1187, when William was fourteen years old, and Sophie twenty-five; nevertheless, this union ended soon: Sophie died shortly after in that year.

On 9 August 1202 William married Berta, daughter of the Marquess Bonifacio di Clavesana, Count of Cortemiglia. They had at least three children:

Otto of Montferrat (died 1251), who became Bishop of Porto, and Cardinal in 1227, may have been a son of William VI; whether he was legitimate or not is uncertain.


  • Caravale, Mario (ed). Dizionario Biografico degli Italiani: LX Grosso – Guglielmo da Forlì. Rome, 2003.
  • Marchesi di Monferrato: Guglielmo VI.
Preceded by
Boniface I
Margrave of Montferrat
Succeeded by
Boniface II

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