As we’re throwing all groundless myths into the mix along with facts, this is generally assumed to be the time of the warlord Arthur. King Arthur was obviously a busy man as according to myths he lived all over the country, and was born in Cornwall, Carmarthen, Carlisle and Edinburgh.
Liverpool can proudly say we have... no connection whatever though. The closest we get is the references to his knights, Gawain questing on the Wirral in the poem Gawain and the Green Knight, and that Owaine, son of Urien ( wife of Morgan le Fay), was a supposed king of Rheged and alleged knight of Camelot.
Taliesin the poet did write about Urien so we have that to grasp frantically on to as a link. We do also have the theme park of Camelot at Charnock Richard up the road but that doesn’t really count.
... and the fact that Lancelot allegedly got his sword from Martin Mere in some myths, but as Lancelot is a much later French addition to the myth, and the RSPB would disapprove, we’ll leave that one aside too.
We don’t know a great deal about Rheged, apart from the fact it is thought the occupants spoke mostly Scots Gaelic, and there is no evidence of any great import connected to the Mersey, so we can continue swiftly through the years to the expansion of Mercia in the seventh century ( after a short sojourn of twenty years or so under the control of Northumbia), when Merseyside found itself under new rulers again. The Anglo-Saxons under Æthelfrith, king of Northumbria, laid waste to Chester around 616. Takes all sorts.
Æthelfrith withdrew, leaving the area west and south of the Mersey to become part of Mercia, and Anglo-Saxon settlers took over Wirral except the northern tip. Many of Wirral's modern villages, such as Willaston, Eastham and Sutton, were established and named at this time. Whether the villagers themselves even noticed the change in overlord is a matter of pure conjecture. Unless they got laid waste to of course. Laying waste seems to have been a popular hobby.