Robert de Ferrers, 6th Earl of Derby (1239–1279) was an English nobleman. He was born at Tutbury Castle in Staffordshire, England, the son of William de Ferrers, 5th Earl of Derby, by his second wife Margaret de Quincy (born 1218), a daughter of Roger de Quincy, 2nd Earl of Winchester and Helen of Galloway. Early years In 1249, at the age of 10, he married the seven-year-old Mary (or Marie), daughter of Hugh XI of Lusignan Count of La Marche, the eldest of Henry III's half-brothers, at Westminster Abbey. This arranged marriage is an indication of Henry's high regard for Robert's father. William died in 1254, so Robert became a knight and inherited the title while he was still a minor. He and his estates became a ward of Prince Edward. In 1257, Edward sold the wardship to the queen and Peter of Savoy for 6000 marks, which might have been a source of the later antipathy of Ferrers for the prince. Inheritance Robert came of age in 1260 and took possession of the vast estates he inherited. The first of these passed to him from his Norman ancestors, a large part of Derbyshire that included the area later known as Duffield Frith, together with parts of Staffordshire and Nottinghamshire. In addition, he received Chartley Castle in Staffordshire, and all Lancashire between the Ribble and the Mersey. This came from the estate of Ranulph de Blondeville, 4th Earl of Chester, whose sister, Robert's grandfather had married. By careful management, the estate had become worth around £1500, which meant that the Ferrers family was among the wealthiest in the country. However, the estate was crippled by charges arising from William's death. Firstly a third of its worth was accounted for by his mother's dower, which included the major asset of Chartley. Nearly half was supporting a debt of around £800 incurred by his father, which the exchequer was calling in. To pay this he had taken a further loan, possibly from Jewish financiers in Worcester. Finally, there was provision for his brother William and his wife Mary, who held two manors herself. It would seem that before taking his inheritance his only income had been the maritagium bestowed by King Henry. Baronial unrest Unlike his predecessors, Robert was impetuous and violent, in part, perhaps, because he had inherited a severe form of gout from his grandfather. He was also unreliable and