Burhs had official status recognised by grants such as the right to mint coinage. In Wessex, these fortified communities were geographically distributed so that, in the period when the Burghal Hidage was compiled, everyone in Wessex lived within a day's march of a place of refuge.
Burhs were supported by the labour of the inhabitants of the burghal district, which was assessed by hides. In regions of medieval England outside the Danelaw, the hide was a unit of land defined according to its agricultural yield and taxable potential rather than its area. The areas of hides ranged from 15 to 30 modern acres (6 to 12 hectares). One hide was assumed to support one household. In wartime, five hides were expected to provide one fully armed soldier, and one man from every hide was to provide garrison duty for the burhs and to help in their initial construction and upkeep. The continued maintenance of the burhs, as well as ongoing garrison duty, was also probably supplied by those inhabitants of the new burhs which were planned by the king as new towns. In this way the economic and military functions of the larger burhs were closely interlinked.
The order of citation of the individual burhs in the document, in a clockwise circuit around Wessex rather than on a shire by shire basis, indicates that at the time of the original composition of the document all the burhs were seen as being part of a single system. The defining characteristic of this system is that these fortified sites would have all been built at one occasion to serve a single strategic end, in that the functions of all the individual components of the system complemented the functions of each of the others. It follows that it cannot have originated, for instance, as a core number to which others were added at a later date. By the early 10th century this system was already long out of date and overtaken by events. It is not likely therefore to have survived as a viable and effective system to be recorded as such in the Burghal Hidage after 914. There would, furthermore, have been no reason to add Buckingham to a system which by 914 was already redundant in the rapidly-evolving political situation of the times. There are therefore good grounds for suggesting that the system (and therefore the document which describes it) is considerably earlier in date.
Work on the minting patterns of the coinage of the period has shown that King Alfred was in control of London and the surrounding area until c.877, exactly the time when the Vikings are recorded as partitioning Mercia and taking control of its eastern extent. Thereafter the coins minted in London are in the name of the Mercian King Ceolwulf alone. After his decisive defeat of the Vikings at the battle of Edington in early 878, Alfred was once again able to take the offensive. His victory must have earned him wide acclaim. It is this juncture which seems the most appropriate time for the start of the planning and construction of the system of burhs recorded in the Burghal Hidage. Throughout 878 Guthrum’s Vikings were in control of Mercia and, arguably, London, with his base in Cirencester. The creation of burhs at Oxford and Buckingham at this time fits in with the likelihood that Alfred was able to regain control of this area which he had exercised before being deprived of it as a result of the Viking partition of 877, and their siting demonstrates that he was able to initiate a strategic offensive against the Vikings in Eastern Mercia and London. Alfred’s standing enabled him to impose a level of conscription on the population of his kingdom to construct the burhs, to act as garrisons behind their defences, and to serve in his new army, at a level which was probably not attained again until the Second World War.
The retreat of Guthrum and his band to East Anglia in late 879, and the similar retreat of the Viking army stationed at Fulham (just to the west of London) back to the Continent at the same time (both events recorded in the Anglo-Saxon Chronicle), can be seen as a tactical response to the effectiveness of the strategic offensive posed by the construction of the Burghal system. The ratification of a mutually-agreed boundary to the east of London, in Alfred and Guthrum’s Treaty, between Guthrum’s new Viking kingdom of East Anglia and Alfred’s newly-won territory, can best be ascribed to this time. These developments gave Alfred control of London and its surrounding territory, which included a good length of the strategically-important Watling Street as it approached London. This interpretation is supported by the issue at this time of the special celebratory London Monogram coinage from the London mint, now under the control of Alfred, and by the issue at the same time of coins from Oxford and Gloucester in southern Mercia .
The fact that the Burghal Hidage does not include London, only taken in late 879; that many of the burhs recorded in the document were of a temporary nature and were only replaced by more permanent fortified sites later on; and that its organisation reflects a strategic offensive against the Viking presence in Mercia and London, are factors which argue strongly that the Burghal Hidage is a prescriptive list describing a system which was in process of being planned and implemented before late 879. It is therefore likely to have originated in a context in which the logistics of the system and the means for its implementation and support were being worked out in practice on the ground. The fact that the construction of a burh at Buckingham by Alfred can be logically placed within this strategic scheme at this period (878-9), removes the necessity of having to place the creation of the original version of the Burghal Hidage after the first documentary mention of Buckingham in 914. Its composition can therefore be most appropriately placed in a West Saxon context, rather than one which relates to the formation of burhs and shires in Mercia in the early 10th century – to which situation it has no relevance.
In Wessex a number of the burhs which were part of the system recorded in the Burghal Hidage, and which were merely fortresses rather than fortified towns, were in many cases replaced at a later date by larger fortresses which were fortified towns. The received view of the date of this process is that this took place in the 920s or 930s (in the reign of Athelstan. More recently, arguments have been given which places these changes in the reign of Alfred, possibly in the 890s in response to the new Viking invasions. Examples of this process can be seen in the replacement of Pilton by Barnstaple, and Halwell by Totnes and Kingsbridge in Devon