In 858 Robert joined a rebellion against Charles the Bald. With the Bretons under Salomon he led the Frankish nobles of Neustria and invited Louis the German to invade West Francia and receive their homage. The revolt had been sparked by a marriage alliance between Charles and Erispoe, King of Brittany, and by the investment of Charles’ son, Louis the Stammerer, with the "regnum Neustriae", all which significantly curtailed the powers of both Salomon and Robert. Charles had given Robert the counties of Autun and Nevers in Burgundy; and in 856 Robert had defended Autun from Louis the German. But following Erispoe's assassination in November 857, he and Salomon rebelled against Charles.