Once he had divided up his kingdom, Brutus decided to build a capital. In pursuit of this plan, he visited every part of the land in search of a suitable spot. He came at length to the River Thames, walked up and down its banks and so chose a site suited to his purpose. There then he built his city and called it Troia Nova. It was known by this name for long ages after, but finally by a corruption of the word it came to be called Trinovantum. After Lud, the brother of Cassivelaunus, who fought with Julius Caesar, had seized command of the government of the kingdom, he surrounded the capital with lofty walls and with towers built with extraordinary skill, and he ordered it to be called Kaerlud, or Lud's City, from his own name. [I.17]

Heli had three sons: Lud, Cassivelaunus and Nennius. Lud, the eldest of these, accepted the kingship after his father's death. He was famous for his town-planning activities. He rebuilt the walls of the town of Trinovantum and girded it round with innumerable towers. He ordered the citizens to construct their homes and buildings in such a style that no other city in the most far-flung of kingdoms could boast of palaces more fair. Lud was a warrior king, lavish in arranging feasts. However many other cities he might possess, this one he loved above all and in it he passed the greater part of each year. As a result it was afterwards called Kaerlud and then, as the name became corrupted, Kaerlundein. In a later age, as languages evolved, it took the name London, and later still, when the foreign invaders landed and conquered the country, it was called Lundres. When Lud died his body was buried in the above-named city, near to the gateway which in the British tongue is still called Porthlud after him, although in Saxon it bears the name Ludgate. [III.20]

Geoffrey's double foundation story for LONDON, attributing its existence to both Brutus and Lud, is only the beginning of his attention to the city. Tatlock points out that no other city is as consistently important in the Historia (p. 30). It is presented as a political centre from the start: rulers hold councils and celebrations there, imprison their enemies there, memorialize themselves through its monuments, and are buried there:

Dunvallo died at last having spent forty years in such activities since the day when he took the crown. He was buried in Trinovantum beside that Temple of Concord which he himself had built as a symbol of his own law. [II.17]

In the town of Trinovantum Belinus caused to be constructed a gateway of extraordinary worksmanship, which in his time the citizens called Billingsgate, from his own name. On the top of it he built a tower which rose to a remarkable height; and down below at its foot he added a water-gate which was convenient for those going on board their ships. [III.10]

They seized Elidurus and shut him up in a tower in the town of Trinovantum, setting a guard to watch over him. [III.18]

Cassivelaunus was greatly elated when he had won this second victory. He issued an edict that all the British leaders should assemble with their wives in the town of Trinovantum to do honour to their country's gods who had given them victory over so mighty an Emperor. [IV.8]

Vortigern then took charge of Constans, dressed him up in royal garments and led him off to London. There Vortigern made Constans King, though hardly with the people's approval. [VI.6]

Vortimer... ordered a bronze pyramid to be constructed for him and set up in the port where the Saxons usually landed. After his death his body was to be buried on top of this, in the hope that when the barbarians saw his tomb they would reverse their sails and hurry back to Germany.... However, once he was really dead, the Britons did quite differently, for they buried his body in the town of Trinovantum. [VI.14]

Aurelius set off for the town of London, which the fury of the enemy had certainly not spared. Grieved as he was by the destruction of the town, he collected together from every quarter such citizens as were left alive, and began the task of rebuilding it. It was from that city that he ruled his kingdom, bringing new life to laws which had been allowed to fall into disuse and restoring to their rightful heirs the scattered possessions of long-dead folk. [VIII.9]

When Uther had finally pacified the northern provinces, he moved to London. He ordered Octa and Eosa to be kept in prison there. The next Eastertide, Uther told the nobles of the kingdom to assemble in that same town of London, so that he could wear his crown and celebrate so important a feast-day with proper ceremony. [VIII.19]

Arthur accepted the advice of his retainers and withdrew into the town of London. There he convened the bishops and the clergy of the entire realm and asked their suggestion as to what it would be best and safest for him to do, in the face of this invasion by the pagans. [IX.2]

As soon as Constantine had been crowned, the Saxons and the two sons of Mordred promptly rose against him. They failed in their attempt to overthrow him; and, after a long series of battles, they fled. One of them made his way into London and the other to Winchester, and they took command of those two cities.... The second son of Mordred hid himself in the monastery of certain friars in London. Constantine discovered him and slew him without mercy, beside the altar there. [XI.3-4]

At a certain Whitsuntide court, when King Cadwallo was celebrating the feast in London by wearing the crown of Britain, and all the British leaders and all the kings of the Angles were present except only Oswi, Peanda therefore when up to the King and asked him why Oswi alone had absented himself... [XII.11]

Finally, after forty-eight years, Cadwallo, this most noble and most powerful King of the Britons, become infirm with old age and illness, departed this life on the fifteenth day after the Kalends of December. The Britons embalmed his body... and placed it inside a bronze statue which, with extraordinary skill, they had cast to the exact measure of his stature. They mounted this statue, fully armed, on a bronze horse of striking beauty, and erected it on top of the West Gate of London, in memory of the victory of which I have told you and as a source of terror to the Saxons. Underneath they built a church in honour of St Martin, and there divine services are celebrated for Cadwallo and for others who die in the faith. [XII.13]

It is a religious centre, both before and after the coming of Christianity:

At that time there were twenty-eight flamens in Britain and three archflamens.... At the Pope's bidding, the missionaries converted these men from their idolatry. Where there were flamens they placed bishops and where there were archflamens they appointed archbishops. The seats of the archflamens had been in three noble cities, London, York, and the City of the Legions... [IV.19]

Guithelinus, archbishop of London, is an important figure at the end of the Roman period, VI.2.

It is also the site of intriguing stories, such as the imprisonment of Estrildis, the death of Bladud, and the departure of St Ursula and her 11,000 virgins:

Locrinus duly married Corineus's daughter, whose name was Gwendolen. For all that, he could not forget the love which he felt for Estrildis. He had a cave dug beneath the town of Trinovantum and there he shut Estrildis up.... [II.4]

Bladud was a most ingenious man who encouraged necromancy throughout the kingdom of Britain. He pressed on with his experiments and finally constructed a pair of wings for himself and tried to fly through the upper air. He came down on top of the Temple of Apollo in the town of Trinovantum and was dashed into countless fragments. [II.10]

When he saw the messenger come from Conanus, Dionotus agreed to meet his wishes. He therefore assembled from the various provinces eleven thousand daughters of noblemen, with sixty thousand others born to the lower orders, and commanded them all to come together in the city of London.... the fleet was made ready, the women went on board the ships, and they put out to sea down the River Thames....The ships ran the hazard of the seas and for the most part they foundered.... As [the Huns and Picts] raged along the sea-coast, they met the young women... who had been driven ashoes there. When the men saw how beautiful the girls were, their first intention was to have intercourse with them. When the women refused to permit this, the Ambrones atttacked them and slaughtered most of them there and then. [V.16]

 

It is frequently featured in warfare:

Brennius was moved by what his weeping mother had said.... When Belinus saw him coming with a peaceful look on his face, he threw down his own weapons and ran forward to put his arms round Brennius and kiss him. There and then they became firm friends. Their troops disarmed and they all entered the town of Trinovantum together. [III.7]

Below the waterline in the bed of the River Thames, up which Cassivelaunus planted stakes as thick as a man's thigh and shod with iron and lead, so that Caesar's ships would be gutted as they moved forward.... Had Caesar been able to land with his fleet undamaged, no doubt he would have achieved his aim; but as he cruised up the Thames in the direction of the above-mentioned city of Trinovantum his ships ran upon the stakes I have described and so suffered their moment of sudden jeopardy. Thousands of soldiers were drowned as the river-water flowed into the holed ships and sucked them down. [IV.6-7]

Meanwhile Cassivelaunus was beginning to besiege Trinovantum and was already sacking the villas on the outskirts of the city. When he heard of the arrival of Julius, he abandoned the siege and hurried to meet the Emperor. [IV.9]

As soon as it was realized that Asclepiodotus was the victor, Livius Gallus... withdrew what remained of the Romans into London.... Asclepiodotus lost no time in laying siege to the city.... The Demeti marched in answer to his summons.... They quickly tore down the walls, and once they had forced an entrance they set about killing the Romans. When the Romans saw that they were being slaughtered one after the other, they persuaded Gallus to surrender together with his men and to beg mercy of Asclepiodotus.... [he] was prepared to have mercy on them; but the Venedoti advanced in formation and in one day decapitated the lot of them, beside a brook in the city which from the name of their leader was afterwards called Nantgallum in Welsh, or in Saxon Galobroc. [V.4]

Many were killed on both sides, but the Saxons had the upper hand; for the Britons, who had not expected anything of this sort to happen, had come unarmed and had little chance of offering resistance.... The Saxons went first to London and captured the city. Next they took York, Lincoln and Winchester, ravaging the neighbouring countryside and attacking the peasantry, just as wolves attack sheep which the shepherds have forsaken. [VI.16]

 

Most of the time, Geoffrey seems to be working backwards, inventing the city's history to match his own knowledge of it: Tatlock suggests, for example, that he might have come up with the names Lud and perhaps partly Belinus through the names of the city's gates (p. 31). While there is no official mention of a church of St Martin before 1222, it is likely that Geoffrey is reflecting the existence of a parish that was known in his day when he again back-dates the founding of St Martin's church at Ludgate. Similarly, his account of the tower built by Belinus probably reflects the Norman tower, rather than any actual building of the past (p. 31). It is interesting, given Geoffrey's account of the massacre of Gallus's Romans, that a collection of skulls dating from Roman times has indeed been found in the bed of the Walbrook: the Museum of London featured a picture of them on its website as part of the now-archived Macabre London exhibit, but without Geoffrey's explanation (the accepted explanation today is that these might be the skulls of Londoners massacred during Boudicca's revolt).

Given the city's prominence, it is not surprising that it features prominently in Merlin's prophecies:

Religion shall be destroyed a second time and the sees of the primates will be moved to other places. London's high dignity shall adorn Durobernia: and the seventh pastor of York will be visited in the realm of Armorica. [VII.3]

He who will achieve these things shall appear as the Man of Bronze and for long years he shall guard the gates of London upon a brazen horse. [VII.3]

Then a Tree shall spring up on the top of the Tower of London. It will be content with only three bracnhes and yet it will overshadow the whole length and breadth of the island with the spread of its leaves.[VII.3]

London shall mourn the death of twenty thousand and the Thames will be turned into blood.[VII.3]

... from a town in Canute's Forest a girl shall be sent to remedy these matters by her healing art.... she shall carry the Forest of Caledon in her right hand and in her left the buttressed forts of the walls of London. [VII.4]

London will view this with envy and will increase her own fortifications threefold. The River Thames will surround London on all sides and the report of that engineering feat will cross the Alps. [VII.4]

In the days of the Fox a Snake shall be born and this will bring death to human beings. It will encircle London with its long tail and devour all those who pass by. [VII.4]

Then the Thames shall begin to flow again. It will gather together its tributaries and overflow the confines of its bed. It will submerge nearby towns and overturn the mountains in its course. It will join itself to the Springs of Galabes, filled as they are to the very brim with wickedness and deceit. [VII.4]