Ceawlin was active during the last years of the Anglo-Saxon expansion, with little of southern England remaining in the control of the native Britons by the time of his death.

The historical accuracy and dating of many of the events in the later Anglo-Saxon Chronicle have been called into question, and his reign is variously listed as lasting seven, seventeen, or thirty-two years.

These peoples captured territory in the east and south of England, but at about the end of the fifth century, a British victory at the battle of Mons Badonicus halted the Anglo-Saxon advance for fifty years.

[5] The peace following the battle of Mons Badonicus is attested partly by Gildas, a monk, who wrote De Excidio et Conquestu Britanniae or On the Ruin and Conquest of Britain during the middle of the sixth century.

[6] The Anglo-Saxon Chronicle is the other main source that bears on this period, in particular in an entry for the year 827 that records a list of the kings who bore the title "bretwalda", or "Britain-ruler".

Though there are many unanswered questions about the chronology and activities of the early West Saxon rulers, it is clear that Ceawlin was one of the key figures in the final Anglo-Saxon conquest of southern Britain.

Almost twenty annals describing Cerdic's campaigns and those of his descendants appear interspersed through the next hundred years of entries in the Chronicle.

Both the list and the Chronicle are influenced by the desire of their writers to use a single line of descent to trace the lineage of the Kings of Wessex through Cerdic to Gewis, the legendary eponymous ancestor of the West Saxons, who is made to descend from Woden.

Some of the problems in the Wessex genealogies may have come about because of efforts to integrate Ceawlin's line with the other lineages: it became very important to the West Saxons to be able to trace the ancestors of their rulers back to Cerdic.

The entry says "Here Ceawlin and Cutha fought against Aethelberht and drove him into Kent; and they killed two ealdormen, Oslaf and Cnebba, on Wibbandun."

[28][29] David Cooper proposes Wyboston, a small village 8 miles north-east of Bedford on the west bank of the Great Ouse.

Wibbandun is often written as Wibba's Dun, which is close phonetically to Wyboston and Æthelberht's dominance, from Kent to the Humber according to Bede, extended across those Anglian territories south of the Wash.

It was this region that came under threat from Ceawlin as he looked to establish a defensible boundary on the Great Ouse River in the easternmost part of his territory.

[13] There are multiple examples of joint kingship in Anglo-Saxon history, and this may be another: it is not clear what Cutha's relationship to Ceawlin is, but it certainly is possible he was also a king.

[31] The annal for 571 reads: "Here Cuthwulf fought against the Britons at Bedcanford, and took four settlements: Limbury and Aylesbury, Benson and Eynsham; and in the same year he passed away."

One possible explanation is that this annal records a reconquest of land that was lost to the Britons in the campaigns ending in the battle of Mons Badonicus.

[27] The annal for 577 reads "Here Cuthwine and Ceawlin fought against the Britons, and they killed three kings, Coinmail and Condidan and Farinmail, in the place which is called Dyrham, and took three cities: Gloucester and Cirencester and Bath.

"[32] This entry is all that is known of these Briton kings; their names are in an archaic form that makes it very likely that this annal derives from a much older written source.

[36] Wansdyke, an early-medieval defensive linear earthwork, runs from south of Bristol to near Marlborough, Wiltshire, passing not far from Bath.

"[13] There is a wood named "Fethelée" mentioned in a twelfth-century document that relates to Stoke Lyne, in Oxfordshire, and it now is thought that the battle of Fethan leag must have been fought in this area.

[37] It also has been used to argue that perhaps, Ceawlin did not win the battle and that the chronicler chose not to record the outcome fully—a king does not usually come home "in anger" after taking "many towns and countless war-loot".

[38] The Anglo-Saxon Chronicle, in an entry for the year 827, repeats Bede's list, adds Egbert of Wessex, and also mentions that they were known as "bretwalda", or "Britain-ruler".

[41] In Ceawlin's case the range of control is hard to determine accurately, but Bede's inclusion of Ceawlin in the list of kings who held imperium, and the list of battles he is recorded as having won, indicates an energetic and successful leader who, from a base in the upper Thames valley, dominated much of the surrounding area and held overlordship over the southern Britons for some period.

When the Ecclesiastical History was written, Æthelbald of Mercia dominated the English south of the Humber, and Bede's view of the earlier kings was doubtless strongly coloured by the state of England at that time.

The lack of gaps between the overlordships of the later bretwaldas has been used to make an argument for Ceawlin's dates matching the later entries in the Chronicle with reasonable accuracy.

The 568 date for the battle at Wibbandun is thought to be unlikely because of the assertion in various versions of the West Saxon Genealogical Regnal List that Ceawlin's reign lasted either seven or seventeen years.

If this battle is placed near the year 590, before Æthelberht had established himself as a powerful king, then the subsequent annals relating to Ceawlin's defeat and death may be reasonably close to the correct date.

[42] The gap between Ælle and Ceawlin, on the other hand, has been taken as supporting evidence for the story told by Gildas in De Excidio of a peace lasting a generation or more following a Briton victory at Mons Badonicus.

It is possible that some fragmentation of control among the West Saxons occurred at Ceawlin's death: Ceol and Ceolwulf may have been based in Wiltshire, as opposed to the upper Thames valley.