Quintus Petillius Cerialis Caesius Rufus, otherwise known as Quintus Petillius Cerialis (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 crushed the rebellion of Julius Civilis and returned to Britain as its governor.
Because he probably succeeded Caesius Nasica as commander of Legio IX Hispana, and since brothers are often attested as serving in succession in the same post, Anthony Birley suggests that Cerialis was the younger brother of Nasica, and had been adopted by Petillius Rufus, who was known as praetor in AD 28. However, in his monograph of naming practices in the first centuries of the Roman Empire Olli Salomies argues that Cerialis was actually the biological son of Petillius Rufus by a Caesia, who may have been the daughter of a Caesius Cerialis, and Caesius Nasica would not be his brother, "but a close relative."
His first important assignment was as legate of Legio IX Hispana (Ninth Iberian Legion) in the Roman province of Britannia, under governor Gaius Suetonius Paulinus. In the defeat of the 60/61 rebellion led by Queen Boudica of the Iceni, Cerialis suffered a serious defeat when attempting to relieve the city of Camulodunum (Colchester), which was taken by the Britons before he arrived. "The victorious enemy met Petilius Cerialis, commander of the ninth legion, as he was coming to the rescue, routed his troops, and destroyed all his infantry. Cerialis escaped with some cavalry into the camp, and was saved by its fortifications." 
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.
This success and his brother-in-law's trust gave him the command of XIV Gemina, then stationed in the difficult province of Germania Inferior. Again, Cerialis had to deal with a local revolt, the Batavian rebellion, in which the local tribes, led by Julius Civilis, a romanized prince, besieged two Roman legions at Xanten. Cerialis was again successful and received honours from Vespasian, which included his first consulate.
In 71, Cerialis was appointed governor of Roman Britain, bringing the II Adiutrix with him to the province. He was supported by Gnaeus Julius Agricola, commander of XX Valeria Victrix.
As governor, Cerialis campaigned against the Brigantes of northern England. In 74, Cerialis left Britain; a military diploma dated 21 May 74 attests he was consul a second time, with Titus Clodius Eprius Marcellus as his colleague.
According to the 1911 Encyclopædia Britannica, "Tacitus says that he was a bold soldier rather than a careful general, and preferred to stake everything on the issue of a single engagement. He possessed natural eloquence of a kind that readily appealed to his soldiers. His loyalty to his superiors was unshakable".