On the assassination of Grimoald IV, Sico succeeded to the princely throne.
He did, however, remove the body of the Neapolitan patron saint, Januarius, who was originally from Benevento.
It was also Sico who founded a line of rulers at Capua by bestowing that ancient fortress on Landulf I as gastald.
Landulf honoured his benefactor by naming his first castle Sicopolis.
His daughter Itta (also spelled Ita or Itana) married Guy I, Duke of Spoleto.