After a civil war broke out in Bari, Risone, the archbishop of the city, was murdered (1117) and the princess of Taranto, Constance of France, was imprisoned at Giovinazzo (1119) by Grimoald and Alexander, Count of Conversano.
In June 1123, a Byzantine-inspired blue diploma with gold script calls him Grimoaldus Alferanites gratia Dei et beati Nikolai barensis princeps.
With a fleet of sixty ships, George of Antioch blockaded the Bariot harbour and besieged Grimoald for months from Spring to August, when the prince finally gave in.
When, the next year (1130), Roger sought the royal title, receiving an honour higher than that of prince (as the rulers of Capua and Bari held) was one of his many motives.
It seems, from the dating of the events, that the prince of Bari who rescued the saintly Giovanni di Matera from prison and then demanded that the holy man give an account of his theology to prove its orthodoxy was Grimoald.