William of Montreuil

William of Montreuil (; died after 1068), was an Italo-Norman freebooter of the mid-eleventh century who was briefly Duke of Gaeta. He was described by Amatus of Monte Cassino as "an exceptional knight, small in stature, who was very robust, strong, valiant" and by Orderic Vitalis as 'the good Norman' .

Career He was a son of William fitz Giroie Lord of Échauffour and Montreuil-l'Argillé and Emma de Tannei, daughter of Walchelin de Tannei. By a charter to the Abbey of Saint-Evroul in 1050, William was still in Normandy at that time. Like his father and brother he granted all the monasteries he possessed, in return "for no small sum", to the abbey of Saint-Evroul. With his brother Arnold consenting, he granted the abbey his mills, farms and fisheries. At some point he joined forces with Richard I Drengot, who became Prince of Capua in 1058. Richard both adopted William as his son and gave him his daughter's hand in marriage. The prince then ceded control of Gaeta to William, but he soon revolted and attempted to repudiate his wife after which he planned to marry Duchess Maria, widow of Atenulf I, the former Duke of Gaeta. He joined together with Count Atenulf of Aquino, Lando, Count of Traietto, and Lando's son Peter to free themselves of Prince Richard's control and keep their castles. William obtained some help from friends in Apulia consisting of donations and knights to support him and returned to hold Traetto against the prince. He arranged for Maria to wed his son, Jordan (who he had also made a prince), which offer the duchess readily accepted. apparently emboldened by the lands originally given him by the prince had since been regranted by the pope. William assumed he could count on the pope opposing his master Richard, so he began burning the prince's towns. Not being able to locate William or his troops, Jordan and his knights raided William's territories carrying off a great deal of plunder. since William had been away at the time. He was gonfalonier of the Roman troops, carrying the banner of St. Peter in the conquest of the fertile plains of Campania. The inhabitants were schismatics, a splinter group who had cut themselves off from the Catholic Church. William, by force of arms, compelled them to accept the authority of the church. An Islamic historian called William de Montreuil the "Captain of the Cavalry of Rome" at the Siege of Barbastro in 1063.

William was, like many of his kinsmen, a benefactor to the Abbey of Saint-Evroul in Normandy. When visited by his father, he sent back a great deal of gifts and money to Saint-Evroul with his father and his companions. William gave to his cousin, Robert de Grandmesnil, former abbot of Saint-Evroul, half the town of Aquino to support him and his monks, the brothers having recently been exiled from Normandy. According to the chronicler Amatus of Montecassino, William died in Rome of a "burning fever."