Coilus was a legendary

Legend

A legend is a narrative of human actions that are perceived both by teller and listeners to take place within human history and to possess certain qualities that give the tale verisimilitude...

 king of the Britons during the time of the Roman

Roman Empire

The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

 occupation

Military occupation

Military occupation occurs when the control and authority over a territory passes to a hostile army. The territory then becomes occupied territory.-Military occupation and the laws of war:...

 of Britain

Roman Britain

Roman Britain was the part of the island of Great Britain controlled by the Roman Empire from AD 43 until ca. AD 410.The Romans referred to the imperial province as Britannia, which eventually comprised all of the island of Great Britain south of the fluid frontier with Caledonia...

 as recounted in Geoffrey of Monmouth

Geoffrey of Monmouth

Geoffrey of Monmouth was a cleric and one of the major figures in the development of British historiography and the popularity of tales of King Arthur...

's pseudohistorical Historia Regum Britanniae

Historia Regum Britanniae

The Historia Regum Britanniae is a pseudohistorical account of British history, written c. 1136 by Geoffrey of Monmouth. It chronicles the lives of the kings of the Britons in a chronological narrative spanning a time of two thousand years, beginning with the Trojans founding the British nation...

. He was the son of King Marius

Marius of Britain

Marius was a legendary king of the Britons during the time of the Roman occupation of Britain, as recounted in Geoffrey of Monmouth's pseudohistorical Historia Regum Britanniae. He was the son of King Arvirargus and ruled following his father's death....

 and ruled following his father's death.

According to Geoffrey, Coilus was brought up in Rome

Rome

Rome is the capital of Italy and the country's largest and most populated city and comune, with over 2.7 million residents in . The city is located in the central-western portion of the Italian Peninsula, on the Tiber River within the Lazio region of Italy.Rome's history spans two and a half...

 and favoured the company of Romans in Britain. Throughout his reign he paid Rome its tribute

Tribute

A tribute is wealth, often in kind, that one party gives to another as a sign of respect or, as was often the case in historical contexts, of submission or allegiance. Various ancient states, which could be called suzerains, exacted tribute from areas they had conquered or threatened to conquer...

 without question. In Britain, he allowed the nobles peace and granted them large gifts. He was succeeded by his only son, St Lucius

Lucius of Britain

Saint Lucius is a legendary 2nd-century King of the Britons traditionally credited with introducing Christianity into Britain. Lucius is first mentioned in a 6th-century version of the Liber Pontificalis, which says that he sent a letter to Pope Eleuterus asking to be made a Christian...

.