The Once and Future King is a novel, but it draws upon a tradition of Arthurian literature known as the "Matter of Britain" writings. These writings were at their most popular during the fourteenth century: readers were obsessed with the characters they knew from these stories and produced multiple new versions of tales about all of them. Many of these stories explored or elucidated a political or social issue of the time. The idea of London as a "new Troy" is one such element.

The idea of Brutus as the mythological founder of London is generally credited to Geoffrey of Monmouth, but it is probable that he did not invent it wholesale. He suggested that Brutus, a descendant of Aeneas, came to Britain to found London, therefore suggesting a direct line of connection between London and Troy. This gave London a certain legitimacy, and the nobility of England at this time sought legitimacy and would often claim to be descended from Trojans. This was important because, it must be remembered, the ruling class of England in the fourteenth century were largely immigrants from France, who had trodden down and suppressed the existing Anglo-Saxon populace. Claiming a connection to Troy, then, allowed them to argue that they were supposed to be there and supposed to rule, because they were from the same noble bloodline as Aeneas and therefore had an ancient entitlement to rule. This was also important during the turmoil of the fourteenth century as an ongoing war with France raged. The nobles—now mostly English-speaking, as indicated by the language in which most "matter of Britain" material is written—wanted to create a history for themselves which enabled them to be English, rather than French, while still maintaining a line of noble blood which secured their legitimacy to rule. By declaring themselves to be descendants of Brutus, the Trojan founder of London, this was achieved.

First, The Once and Future King by T. H. White, is not a myth but a novel based on a combination of earlier literate retellings (primarily Malory) of Arthurian stories that in their turn were based on oral epos. How stories came into such traditions is extremely complicated; as we have no access to the earliest oral strata of the stories, any evaluation of how and when given elements moved into the cycle are, at best, speculative.

The Trojan theme follows Virgil's Aeneid in considering the Romans descendants of the Trojans. Just as Rome was, in a sense, a second Troy, so too was London. Malory may well have been asserting the importance of England as a legitimate successor to Rome with this mythic foundation story, giving London a pedigree on par with Paris, Byzantium, Rome, and other major cities. Often foundation myths are intended as patriotic ways of emphasizing the importance of a country or city.