Complex sentence: He came from the powerful equestrian family of the Erucia and his grandfather Sextus Erucius Clarus was consul in AD 146 and before that City Prefect of Rome.
Split into simpler sentences: He came from the powerful equestrian family of the Erucii. His grandfather, Sextus Erucius Clarus, was consul in AD 146, and before that City Prefect of Rome.