When the Normans besieged Bari in 1068–71, Argyritzos led the faction that favoured seeking terms. On 18 July 1070, the leader of the opposite faction, Bisantius Guirdeliku, was assassinated through the "treachery" of Argyritzos, according to the "Annales Barenses" and the "Annales Lupi Protospatharii". Still, the city held out for another nine months. Argyritzos appears to have inherited a leading position following its surrender on favourable terms to the Norman leader Robert Guiscard.