The Anglo-Saxon Chronicle provides a pedigree tracing Cerdic's ancestry back to Wōden and the antediluvian patriarchs.
Kenneth Sisam has shown that this pedigree resulted from a process of elaboration upon a root pedigree borrowed from the kings of Bernicia, and hence before Cerdic himself it has no historical basis.

J.N.L. Myres noted that when Cerdic and Cynric first appear in the Anglo-Saxon Chronicle in s.a.
495 they are described as ealdormen, which at that point in time was a fairly junior rank.
Myres remarks that
It is thus odd to find it used here to describe the leaders of what purports to be an independent band of invaders, whose origins and authority are not otherwise specified.
It looks very much as if a hint is being conveyed that Cerdic and his people owed their standing to having been already concerned with administrative affairs under Roman authority on this part of the Saxon Shore.

Furthermore, it is not until s.a.
519 that Cerdic and Cynric are recorded as "beginning to reign", suggesting that they ceased being dependent vassals or ealdormen and became independent kings in their own right.

Summing up, Myres believed that
It is thus possible...to think of Cerdic as the head of a partly British noble family with extensive territorial interests at the western end of the Litus Saxonicum.
As such he may well have been entrusted in the last days of Roman, or sub-Roman authority with its defence.
He would then be what in later Anglo-Saxon terminology could be described as an ealdorman...If such a dominant native family as that of Cerdic had already developed blood-relationships with existing Saxon and Jutish settlers at this end of the Saxon Shore, it could very well be tempted, once effective Roman authority had faded, to go further.
It might have taken matters into its own hands and after eliminating any surviving pockets of resistance by competing British chieftains, such as the mysterious Natanleod of annal 508, it could 'begin to reign' without recognizing in future any superior authority.

Cerdic's father Elesa has been identified by some scholars with the Romano-British Elasius, the "chief of the region", met by Germanus of Auxerre.
The Anglo-Saxon Chronicle provides a pedigree tracing Cerdic's ancestry back to Wōden and the antediluvian patriarchs. Kenneth Sisam has shown that this pedigree resulted from a process of elaboration upon a root pedigree borrowed from the kings of Bernicia, and hence before Cerdic himself it has no historical basis.
J.N.L. Myres noted that when Cerdic and Cynric first appear in the Anglo-Saxon Chronicle in s.a. 495 they are described as ealdormen, which at that point in time was a fairly junior rank. Myres remarks that
It is thus odd to find it used here to describe the leaders of what purports to be an independent band of invaders, whose origins and authority are not otherwise specified. It looks very much as if a hint is being conveyed that Cerdic and his people owed their standing to having been already concerned with administrative affairs under Roman authority on this part of the Saxon Shore.
Furthermore, it is not until s.a. 519 that Cerdic and Cynric are recorded as "beginning to reign", suggesting that they ceased being dependent vassals or ealdormen and became independent kings in their own right.
Summing up, Myres believed that
It is thus possible...to think of Cerdic as the head of a partly British noble family with extensive territorial interests at the western end of the Litus Saxonicum. As such he may well have been entrusted in the last days of Roman, or sub-Roman authority with its defence. He would then be what in later Anglo-Saxon terminology could be described as an ealdorman...If such a dominant native family as that of Cerdic had already developed blood-relationships with existing Saxon and Jutish settlers at this end of the Saxon Shore, it could very well be tempted, once effective Roman authority had faded, to go further. It might have taken matters into its own hands and after eliminating any surviving pockets of resistance by competing British chieftains, such as the mysterious Natanleod of annal 508, it could 'begin to reign' without recognizing in future any superior authority.
Cerdic's father Elesa has been identified by some scholars with the Romano-British Elasius, the "chief of the region", met by Germanus of Auxerre.
Cerdic of Wessex