Quintus Petilius Cerialis Caesius Rufus (born ca. AD 30 died after AD 83) was a Roman general and administrator who served in Britain during Boudica's rebellion and who went on to participate in the civil wars after the death of Nero. He later defeated the rebellion of Julius Civilis and returned to Britain as its governor.
His name suggests that he was an adopted son of a Caesius family into the Petilii. His elder brother may have been Caesius Nasica.
His first important assignment was as legate of the Roman legion IX Hispana (Ninth Hispanic Legion) in the Roman province of Britannia, under governor Gaius Suetonius Paulinus. He took part in the defeat of the 60/61 rebellion led by Queen Boudica of the Iceni, although he suffered a serious defeat when attempting to relieve the city of Camulodunum (Colchester), which was destroyed by the Britons. His force, the Ninth Legion, was nearly annihilated in the Battle of Camulodunum as they marched to relieve the colony. By the time they approached the town it had already fallen, and the army was attacked by the full force of the victorious British tribes. They were overwhelmed, and only the cavalry, including Cerialis, managed to escape to a nearby fort. The survivors remained in the fort until joined by Suetonius Paulinus, after his final victory.
As a relative of Vespasian, Cerialis was made a hostage by Vitellius in 69, during the civil wars of the Year of Four Emperors. Cerialis managed to escape disguised as a peasant and joined the Flavian army. He was one of the cavalry leaders that conquered Rome for the approaching Vespasian. His role was to enter Rome via Sabine territory along the Via Salaria.