Titus Flavius Petro was the paternal grandfather of the Roman Emperor Vespasian. He was a son of a contracted labourer, who each summer crossed the Po to assist the Sabines with their harvests.
Petro was born and raised in Reate. He fought for Pompey in the civil war and as a centurion or a volunteer reservist. Leaving the battlefield of Pharsalus Greece, he secured a discharge with a full pardon and became a tax collector. He married a woman called Tertulla (Vespasian’s beloved grandmother) and had a son Titus Flavius Sabinus I.
Source: Suetonius, The Twelve Caesars - Vespasian