About Guillaume de Grandmesnil
Guillaume de Grandmesnil (born around 1055/1060, died between 1100 and 1114) was a Norman baron of Calabria, a member of the Grandmesnil family and related to the House of Hauteville.
William Grandmesnil was the second son of Hugh, lord of Grandmesnil († 1098), one of the companions of William the Conqueror at the Battle of Hastings (1066), and Adelise († 1091) , daughter of Count Yves de Beaumont. He is also the nephew of Robert († 1089), abbot of Saint-Évroult and Santa Maria di Sant 'Eufemia in Calabria, whose half-sister Judith of Evreux († 1076) married in 1062, Roger de Hauteville, Norman conqueror of Muslim Sicily (1061-1091).
According to Orderic Vitalis, William was highly regarded at the court of the king of England had such an attachment to him that he gave him to wife his niece Agnes, daughter of Count Robert de Mortain. But William refused. Driven by the inconstancy and influence of his father, who had acquired many properties in Italy , William decided to go to Apulia, where he arrived around 1080 with some other Normans. In 1081, he participated in the expedition led by Norman Robert Guiscard, Duke of Apulia, Calabria and Sicily, against Dyrrachium (now in Albania), then a Byzantine possession. He participated in the second expedition by Guiscard against the Byzantine Empire (1084-1085) and in July 1085, on the island of Kefalonia, according to Orderic Vitalis, Robert Guiscard, dying, called William with others, to his bedside to maintain his succession. Established in Calabria, he was married at an unknown date Mabille (aka Isabella), a daughter of Robert Guiscard and the Lombard princess Sikelgaite of Salerno, and received at the same time large areas in the Val de Crati in Coscile and Crotone, with fifteen castles.
In 1090 , William Grandmesnil rebelled against the son and successor of Robert Guiscard, Roger Borsa, Duke of Apulia, supporting his brother in law, Prince Bohemond. In 1093, Roger Borsa fell so seriously ill in Melfi that the news of his death spread in many areas. A number of his vassals, including his half brother Bohemond and William Grandmesnil proceeded to revolt. William, seeking to expand his holdings, took Calabria. After the restoration of Roger Borsa and Roger subduing his rebellious vassals, and his half-brother Bohemond, William Grandmesnil at first refused to submit before being compelled by force by the troops of the Duke, assisted by Bohemond and his uncle Roger, Count of Sicily, who arrived at the head of Muslim troops. He lost all his fortresses, and was forced to take refuge with his wife in Byzantium (1094).
In the fall of 1096, he was again in southern Italy, when he sees from Normandy (1102 † 1101 /) brothers Yves and Aubry († AD. 1097) in the ranks of the crusaders led by the Norman Duke Robert Courthose. He decided to accompany them to the Holy Land in the host of Prince Bohemond of Taranto. But June 10, 1098, William and his brother Aubry, frightened by the ardor of the fighting against the Muslims at the siege of Antioch, managed to flee Antioch, besieged by Muslim troops. Returning to the south of Italy (before the capture of Jerusalem by the Crusaders 15 July 1099), William and his brother are excommunicated by Pope Paschal II in January. If the Italo-Norman diplomatic sources have left us traces of his presence in Calabria, we lose track of him after 1100. It seems he and his brother did return to England, as they are castigated at court and sent away by the king for fighting with other courtiers.
From his union with Mabille, daughter of Robert Guiscard, Guillaume Grandmesnil at least two sons:
Guillaume († 1117 or shortly thereafter), who succeeded his father (in 1114 at the latest) but did not survive long. It is still attested in 1117 in a donation to Trinity La Cava that he had married a certain Agatha, the first wife of his father, but it is doubtful.
Robert († AD. 1129), who rebelled in 1120 against Roger II of Sicily with other Calabrian barons. In 1129, he left his army in and gave Roger his fiefs and left the south of Italy to join his family "beyond the Alps" (probably Normandy).