 Constans then moved on to Sicily, oppressed the population, and was assassinated at Syracuse in 668.Vitalian supported Constans' son Constantine IV against the usurper Mezezius and thus helped him attain the throne.As Constantine had no desire to maintain the Monothelite decree of his father, Vitalian made use of this inclination to take a more decided stand against Monothelitism and to win the emperor over to orthodoxy.