Geoffrey called himself Gaufridus Monemutensis which suggests his roots were in Monmouthshire, though he is thought to have lived in Oxford from 1129 to 1151 and in North Wales until his death in 1155. Caerleon is frequently mentioned in "The History" and it seems likely that Geoffrey's early years were spent near the (then) city which he refers to as "The City of the Legions". This title would seem to describe other Roman Cities better, as Caerleon was only ever home to one legion - The Second Augustan Legion - but Geoffrey takes pains to leave us in no doubt that he is referring to Caerleon.

Here, then, are the references made to Caerleon, "The City of the Legions":

BUILT BY BELINUS (390BC)
Belinus, "king of the entire island from sea to sea", returned to Britain after sacking Rome with his brother Brennius and distributing "all the hidden treasures of the citizens among their own troops". He governed his homeland in peace, restoring existing cities "wherever they had fallen into decay" and founding many new ones. "Among the others he which he founded was a certain city on the bank of the River Usk, near to the Severn Sea; this was the capital of Demetia (nowadays South Wales) and for a long time it was called Kaerusc. When the Romans came the earlier name was dropped and it was re-named the City of the Legions, taking its title from the Roman legions who used to winter there."

THE SEAT OF AN ARCHFLAMEN THEN ARCHBISHOP
The seats of the archflamens (spiritual leaders) had been in "three noble cities: London, York and the City of the Legions, the site of which, by the River Usk in Glamorgan, is still shown by its ancient walls and buildings". The Pope sent missionaries and the archflamens were replaced by archbishops. The 28 flamens were replaced by bishops. Kambria or Wales was placed under the City of the Legions.

JULIUS AND AARON MARTYRED
In the days of Emperor Diocletian, Churches were destroyed and Christians persecuted. "Two townsfolk in the City of the legions", Julius and Aaron "stood firm in the battle-line of Christ". They were "torn limb from limb and mangled with unheard-of cruelty". 

(IN THE PROPHECIES OF MERLIN) THE SEAT MOVES TO MENEVIA (ST DAVIDS)
"Menevia shall be dressed in the pall (ecclesiastical vestment) of the City of the Legions…"

THE ARCHBISHOP ADVISES KING AURELIUS TO SEEK MERLIN'S HELP
After defeating Hengist, the Saxon leader, Aurelius decided to build a monument to those "leaders and princes" betrayed by Hengist. "Tremorinus, Archbishop of the City of the Legions, went to the king and said, ' If there is anyone anywhere who has the ability to execute your plan, then Merlin, the prophet of Vortigern, is the man to do it…' "

DUBRICIUS BECOMES ARCHBISHOP AFTER TREMORINUS
"The two metropolitan sees of York and the City of the Legions were without incumbents. With the general consent of his people, whom he wished to consult in this matter, Aurelius gave York to Samson, a most distinguished man who was famous for his great piety. The city of the Legions he bestowed upon Dubricius, whom divine providence had already singled out as one suitable for promotion there."

DUBRICIUS CROWNS ARTHUR
"After the death of Uther Pendragon, the leaders of the Britons assembled from their various provinces in the town of Silchester and there suggested to Dubricius, the Archbishop of the City of the Legions, that as their king he should crown Arthur, the son of Uther.   ...   Dubricius lamented on the sad state of his country. He called the other bishops to him and bestowed the crown of the kingdom upon Arthur."

ARTHUR'S PLENARY COURT
Arthur summoned all the leaders of the lands under his control to a feast in the City of the Legions. "Situated as it is in Glamorganshire, on the River Usk, not far from the Severn Sea, in a most pleasant position, and being richer in material wealth than any other townships, this city was eminently suitable for such a ceremony."

• The buildings are described as a match for Rome.
• The churches of Julius and Aaron are mentioned.
• The city contained a college of 200 learned men.
• Kings from many parts of Europe were invited.
• There was a grand procession.
• Courteous behaviour.
• Knights, famed for bravery, wore arms.
• Women would only give their love to men who had proved themselves three times in battle.
• Knights planned imitation battles on horseback, women watched from the walls.
• The rest played various games, winners had an immense prize from Arthur – but no sign of ill-feeling among the losers. Three days were passed in this way.
• David, the king's uncle became new archbishop of the city. Dubricius went to live as a hermit.
• A letter arrived from the Romans demanding money. Arthur withdrew the kings to a gigantic tower near the entrance to the palace. A long discussion followed, Arthur listened to the kings' advice. All agreed not to pay. A battle strategy was planned. The kings returned to their own countries to make preparations.

GUINEVERE BECOMES A NUN
"However, the Perjurer (Mordred) re-formed his army and so marched into Winchester on the following night. When this was announced to Queen Guinevere, she gave way to despair. She fled from York to the City of the Legions and there, in the church of Julius the Martyr, she took her vows among the nuns, promising to lead a chaste life."

KINOC BECOMES ARCHBISHOP AFTER DAVID
"David, the most holy Archbishop of the City of the Legions, died in the town of Menevia, inside his own abbey.." He was on a visit to his friars there. He was buried in that same church. Kinoc replaced him in the metropolitan see.