The chronology of Ceawlin's life is highly uncertain. 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. The Chronicle records several battles of Ceawlin's between the years 556 and 592, including the first record of a battle between different groups of Anglo-Saxons, and indicates that under Ceawlin Wessex acquired significant territory, some of which was later to be lost to other Anglo-Saxon kingdoms. Ceawlin is also named as one of the eight "bretwaldas", a title given in the Chronicle to eight rulers who had overlordship over southern Britain, although the extent of Ceawlin's control is not known.
Ceawlin died in 593, having been deposed the year before, possibly by his successor, Ceol. He is recorded in various sources as having two sons, Cutha and Cuthwine, but the genealogies in which this information is found are known to be unreliable.
The history of the sub-Roman period in Britain is poorly sourced and the subject of a number of important disagreements among historians. It appears, however, that in the fifth century raids on Britain by continental peoples developed into migrations. The newcomers included Angles, Saxons, Jutes, and Frisians. 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. Near the year 550, however, the British began to lose ground once more, and within twenty-five years, it appears that control of almost all of southern England was in the hands of the invaders.
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. This essay is a polemic against corruption and Gildas provides little in the way of names and dates. He appears, however, to state that peace had lasted from the year of his birth to the time he was writing. 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". That list shows a gap in the early sixth century that matches Gildas's version of events.
Ceawlin's reign belongs to the period of Anglo-Saxon expansion at the end of the sixth century. 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.
Ultimately, the kingdom of Wessex occupied the southwest of England, but the initial stages in this expansion are not apparent from the sources. Cerdic's landing, whenever it is to be dated, seems to have been near the Isle of Wight, and the annals record the conquest of the island in 530. In 534, according to the Chronicle, Cerdic died and his son Cynric took the throne; the Chronicle adds that "they gave the Isle of Wight to their nephews, Stuf and Wihtgar". These records are in direct conflict with Bede, who states that the Isle of Wight was settled by Jutes, not Saxons; the archaeological record is somewhat in favour of Bede on this.
Subsequent entries in the Chronicle give details of some of the battles by which the West Saxons won their kingdom. Ceawlin's campaigns are not given as near the coast. They range along the Thames valley and beyond, as far as Surrey in the east and the mouth of the Severn in the west. Ceawlin clearly is part of the West Saxon expansion, but the military history of the period is difficult to understand. In what follows the dates are as given in the Chronicle, although as noted above, these are earlier than now thought accurate.
The first record of a battle fought by Ceawlin is in 556, when he and his father, Cynric, fought the native Britons at "Beran byrg", or Bera's Stronghold. This now is identified as Barbury Castle, an Iron Age hill fort in Wiltshire, near Swindon. Cynric would have been king of Wessex at this time.
The first battle Ceawlin fought as king is dated by the Chronicle to 568, when he and Cutha fought with Æthelberht, the king of Kent. 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." The location of "Wibbandun", which can be translated as "Wibba's Mount", has not been identified definitely; it was at one time thought to be Wimbledon, but this now is known to be incorrect. This battle is notable as the first recorded conflict between the invading peoples: previous battles recorded in the Chronicle are between the Anglo-Saxons and the native Britons.
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. The annal for 577, below, is another possible example.
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." Cuthwulf's relationship with Ceawlin is unknown, but the alliteration common to Anglo-Saxon royal families suggests Cuthwulf may be part of the West Saxon royal line. The location of the battle itself is unidentified. It has been suggested that it was Bedford, but what is known of the early history of Bedford's names, does not support this. This battle is of interest because it is surprising that an area so far east should still be in Briton hands this late: there is ample archaeological evidence of early Saxon and Anglian presence in the Midlands, and historians generally have interpreted Gildas's De Excidio as implying that the Britons had lost control of this area by the mid-sixth century. 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.
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." 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. The battle itself has long been regarded as a key moment in the Saxon advance, since in reaching the Bristol Channel, the West Saxons divided the Britons west of the Severn from land communication with those in the peninsula to the south of the Channel. Wessex almost certainly lost this territory to Penda of Mercia in 628, when the Chronicle records that "Cynegils and Cwichelm fought against Penda at Cirencester and then came to an agreement."
It is possible that when Ceawlin and Cuthwine took Bath, they found the Roman baths still operating to some extent. Nennius, a ninth-century historian, mentions a "Hot Lake" in the land of the Hwicce, which was along the Severn, and adds "It is surrounded by a wall, made of brick and stone, and men may go there to bathe at any time, and every man can have the kind of bath he likes. If he wants, it will be a cold bath; and if he wants a hot bath, it will be hot". Bede also describes hot baths in the geographical introduction to the Ecclesiastical History in terms very similar to those of Nennius.
Wansdyke, an early medieval defensive linear earthwork, runs from south of Bristol to near Marlborough, Wiltshire, passing not far from Bath. It probably was built in the fifth or sixth centuries, perhaps by Ceawlin.
Ceawlin's last recorded victory is in 584. The entry reads "Here Ceawlin and Cutha fought against the Britons at the place which is named Fethan leag, and Cutha was killed; and Ceawlin took many towns and countless war-loot, and in anger he turned back to his own [territory]." 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.
The phrase "in anger he turned back to his own" probably indicates that this annal is drawn from saga material, as perhaps are all of the early Wessex annals. 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". It may be that Ceawlin's overlordship of the southern Britons came to an end with this battle.
About 731, Bede, a Northumbrian monk and chronicler, wrote a work called the Ecclesiastical History of the English People. The work was not primarily a secular history, but Bede provides much information about the history of the Anglo-Saxons, including a list early in the history of seven kings who, he said, held "imperium" over the other kingdoms south of the Humber. The usual translation for "imperium" is "overlordship". Bede names Ceawlin as the second on the list, although he spells it "Caelin", and adds that he was "known in the speech of his own people as Ceaulin". Bede also makes it clear that Ceawlin was not a Christian—Bede mentions a later king, Æthelberht of Kent, as "the first to enter the kingdom of heaven".
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". A great deal of scholarly attention has been given to the meaning of this word. It has been described as a term "of encomiastic poetry", but there also is evidence that it implied a definite role of military leadership.
Bede says that these kings had authority "south of the Humber", but the span of control, at least of the earlier bretwaldas, likely was less than this. 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, indicate 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. Despite Ceawlin's military successes, the northern conquests he made could not always be retained: Mercia took much of the upper Thames valley, and the north-eastern towns won in 571 were among territory subsequently under the control of Kent and Mercia at different times.
Bede's concept of the power of these overlords also must be regarded as the product of his eighth-century viewpoint. 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. For the earlier bretwaldas, such as Ælle and Ceawlin, there must be some element of anachronism in Bede's description. It also is possible that Bede only meant to refer to power over Anglo-Saxon kingdoms, not the native Britons.
Ceawlin is the second king in Bede's list. All the subsequent bretwaldas followed more or less consecutively, but there is a long gap, perhaps fifty years, between Ælle of Sussex, the first bretwalda, and Ceawlin. 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. According to this analysis, the next bretwalda, Æthelberht of Kent, must have been already a dominant king by the time Pope Gregory the Great wrote to him in 601, since Gregory would have not written to an underking. Ceawlin defeated Æthelberht in 568 according to the Chronicle. Æthelberht's dates are a matter of debate, but recent scholarly consensus has his reign starting no earlier than 580. 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 has 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. In any case, the battle with Æthelberht is unlikely to have been more than a few years on either side of 590. 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.
Æthelberht of Kent succeeds Ceawlin on the list of bretwaldas, but the reigns may overlap somewhat: recent evaluations give Ceawlin a likely reign of 581–588, and place Æthelberht's accession near to the year 589, but these analyses are no more than scholarly guesses. Ceawlin's eclipse in 592, probably by Ceol, may have been the occasion for Æthelberht to rise to prominence; Æthelberht very likely was the dominant Anglo-Saxon king by 597. Æthelberht's rise may have been earlier: the 584 annal, even if it records a victory, is the last victory of Ceawlin's in the Chronicle, and the period after that may have been one of Æthelberht's ascent and Ceawlin's decline.
Ceawlin lost the throne of Wessex in 592. The annal for that year reads, in part: "Here there was great slaughter at Woden's Barrow, and Ceawlin was driven out." Woden's Barrow is a tumulus, now called Adam's Grave, at Alton Priors, Wiltshire. No details of his opponent are given. The medieval chronicler William of Malmesbury, writing in about 1120, says that it was "the Angles and the British conspiring together". Alternatively, it may have been Ceol, who is supposed to have been the next king of Wessex, ruling for six years according to the West Saxon Genealogical Regnal List. According to the Anglo-Saxon Chronicle, Ceawlin died the following year. The relevant part of the annal reads: "Here Ceawlin and Cwichelm and Crida perished." Nothing more is known of Cwichelm and Crida, although they may have been members of the Wessex royal house – their names fit the alliterative pattern common to royal houses of the time.
According to the Regnal List, Ceol was a son of Cutha, who was a son of Cynric; and Ceolwulf, his brother, reigned for seventeen years after him. 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. This split also may have contributed to Æthelberht's ability to rise to dominance in southern England. The West Saxons remained influential in military terms, however: the Chronicle and Bede record continued military activity against Essex and Sussex within twenty or thirty years of Ceawlin's death.