Robert I, known as Robert the Frisian, was count of Flanders from 1071 to his death in 1093. He usurped the countship after defeating his nephew Arnulf III and his allies, Robert's sister Matilda and King Philip I of France. He made peace with Philip, who became his stepson-in-law, but remained hostile to his sister and brother-in-law, King William the Conqueror of England.
Robert's marriage to Gertrude of Saxony, dowager countess of Holland, in 1063 was not arranged by his father but nonetheless agreed to. His nickname 'the Frisian' was obtained, apparently, when he acted as regent for his stepson, Count Dirk V of Holland Robert and Gertrude had six children: Robert, who became count of Flanders Adela, who became queen of Denmark, Gertrude, who became duchess of Lorraine, Philip, Ogiva, who became abbess of Messines, and Baldwin. On his deathbed in 1070, Baldwin VI left Flanders to his elder son, Arnulf III, and Hainaut to the younger son, Baldwin, with the provision that if either preceded the other in death, he would inherit the other's county as well. Baldwin VI further entrusted Robert, his brother, with the safeguard of Arnulf III, who was still a minor, to which Robert gave his oath of homage and solemn promise to protect his nephew Arnulf. Richilde, Arnulf's mother, was to be regent until Arnulf came of age.
Count of Flanders
Despite the oath, Robert disputed the succession of his nephew Arnulf III upon Baldwin VI's death and entered Ghent with the intent of taking Flanders for himself. Richilde appealed to King Philip I of France who summoned Robert to appear before him. Robert refused and continued his war with Richilde at which point Philip I amassed an army which he brought to Flanders. His army was accompanied by Norman troops, probably sent by Robert's sister, Queen Matilda, and led by William FitzOsborn. William had an interest in marrying Richilde but he was killed in battle at Cassel on 22 June 1071. In that engagement Robert's forces were ultimately victorious but Robert himself was captured and his forces in turn captured Countess Richilde. Both were freed in exchange and the battle continued to its conclusion. Among the dead was Arnulf III, killed by Gerbod the Fleming, 1st Earl of Chester, who apparently fought for Robert. As a result of the battle Robert claimed the countship of Flanders. Countess Richilde and her son Baldwin returned to Hainaut but continued to instigate hostilities against Robert. Count Robert eventually gained the friendship of King Philip I of France by offering him the hand in marriage of his stepdaughter, Bertha of Holland. As a part of their negotiations Corbie, an important trade center on the border between Flanders and lesser France, was returned to royal control. Unlike his father's reign, under Count Robert, Flanders no longer had peaceful ties to Normandy and became a refuge for William the Conqueror's enemies, including his rebellious son Robert Curthose in 1078. In 1085 Robert the Frisian, along with his son-in-law Canute IV of Denmark, planned a naval attack on England, but after Cnut's assassination the plan was never carried out. Taking a considerable armed escort Robert the Frisian made a pilgrimage to Jerusalem in 1086 and on the return trip home spent time assisting the Byzantine Emperor against the Seljuq Turks. In one battle Robert and three of his companions rode ahead of the main army charging the forces under the command of Kerbogha, whose forces the Christians scattered completely. Robert died 13 October 1093.
