In short answer, none of them probably didn't have to "verify" London (Londinium)'s ancient foundation, since the physical ruins of Roman continued to be existed well into the 9th century, as illustrated by /u/BRIStoneman before in: (Part of the question in the AMA thread on Assassin Creed: Valhalla) In the game, there are many roman structures still standing, in London for example there s a relatively intact amphitheatre, a triumph arch, huge statues, roman temples and an aqueduct. How historically correct is that for the time AC Valhalla is set?
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In the 9th century, Anglo-Saxon historical writings also had the tradition in common that London had already existed as a fortified city in the 5th century. Anglo-Saxon Chronicle (MS A) states in the entry of 457 AD:
"Here Hengest and Æsc [legendary leaders of the Saxons] fought against the Briton in the place which is called Crayford, and there killed 4,000 men; and the Britons then abandoned the land of Kent and in great terror fled to the stronghold of London (The translation is taken from: [Swanton trans. 2000: 12])."
Add. References:
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