The point at which Ermin Street – leading from Silchester to other important Roman colonies of Cirencester and (thence to) Gloucester, and linking in to other major roads, including one to London – swung north to a crossing of the Thames, was obviously a strategic location, particularly once the river became a boundary between Wessex and Mercia. Substantial Roman settlement in the vicinity is evidenced, but equally important was that Cirencester, not far off, was one of the larger cities of Roman Britain, giving rise to the suspicion that the Thames was then being used for communication and perhaps even commerce; there may even have been a Roman bridge. Though the Roman road seems to have fallen into disrepair in the Early Middle Ages, the route and a crossing point – not necessarily the Roman one – continued in use. This was where Cricklade, whose name is thought to refer to a place by a river crossing, was established, around a junction where a branch off Ermin Street headed westwards to Malmesbury and then Bath. London-Gloucester traffic using Ermin Street thus came to be routed through Cricklade, doubtless to its advantage. There is some indication the Thames may itself have been diverted to better service Cricklade, which must have preceded the construction of the medieval bridge (not on the site of the Roman one).

Cricklade is mentioned in 903, which suggests occupation in the area, but comes to prominence as one of a set of defensive burhs listed in a document, named by historians the Burghal Hidage, believed drawn up between 911 and 919. Some of these were created hurriedly by Alfred in 878/79 to combat the Danish incursion; Cricklade may have been one of that initial batch, for Danish forces were encamped at Cirencester that year. Whether it was put up on mostly agricultural land of an estate, Chelworth, that was wholly acquired by a later king, or situated to protect an existing settlement near the river crossing is one of those uncertainties that infest Cricklade's history. The burh's initial role as defence and refuge may or may not have been complemented, from the outset, by one as a permanent centre of expanded settlement and goods redistribution; one indication of this secondary role subsequently developing is that minting took place there during the reign of Athelstan (925-39). After the immediate Viking threat had diminished, the original ditch-rampart defences were strengthened with stone walls, perhaps by Ethelred, partly dismantled probably by Cnut, but refortified strongly enough during the Anarchy, by a supporter of the empress, that it could be perceived as a castle – though whether this was simply an elaboration of the burh fortifications, or a structure somewhere outside them, remains a matter of debate. The burh was scientifically designed, using the standard measure of the perch, not just for defence but for settlement – that is, to provide both refuge for locals and resident manpower to support defence. Its interior was laid out with streets, a grid pattern being identifiable in the eastern half, with the main north-south street – the future High Street, but perhaps originally a Roman road linking Ermin Street to the river crossing. However, it is uncertain whether this pattern was part of the original design of the burh, or whether that design incorporated only the roads that lead to the compass-oriented gates into the burh, acquiring the appearance of a grid later, as the site became more settled.

The south-west quadrant incorporated a church, first mentioned in 973 (and again in Domesday) and later evidenced as having the unusual dedication to St. Sampson, a saint of more significance in Wales and Brittany than in England. Built on the highest point of the site, the church is not as close to the crossroads nor to the High Street as might be expected in a planned town; it might have replaced an earlier church or chapel associated with Chelworth, perhaps in the time of Alfred's grandson, Athelstan, a reputed founder of several churches in Wessex, who is known to have acquired from a Breton source some relics of St. Sampson and may conceivably have donated one to Cricklade's church, on the occasion of a rebuild and re-dedication. A stone church is mentioned there ca.973, and fragments of eleventh or even tenth century stonework survive in the fabric, although the church underwent a further rebuild in the twelfth century and expansion in the thirteenth.

An open area on the north side of the church has been interpreted as a marketplace; a street, running from the north-south street, passed between it and the churchyard before heading out towards Malmesbury. That the junction of the High Street with the western arm to Malmesbury and eastern arm from London does not quite align into a crossroads may suggest the marketplace could have straddled the north-south road, with East Street and West Street running into it, the former perhaps realigned slightly for the purpose. This quadrant of Cricklade may represent a pre-burh settlement, incorporating what may have been an existing north-south road and conceivably even a royal residence. The north-west quadrant seems to have been left undeveloped, perhaps to accommodate refugees from neighbouring rural areas, along with their livestock, in times of danger.

The continued urban status of Cricklade is evidenced by the presence of a mint from 979 to 1100, the same period that saw a rebuilding of the church. Domesday associates burgesses with Cricklade, which was then under the shared lordship of the king and Westminster Abbey. It was also recognized as a borough in the fourteenth century – at least for purposes of determining its taxation rate – and as a villa mercatoria for purposes of representation in the parliament of 1275. At the same time its assets were considered a manor and administered accordingly; yet this manor comprised only the borough, whose residents held in common no manorial land other than a meadow beside the Thames, which was parcelled out per burgage, so that parcels were individually conveyable, though grazing was treated as a common right of burgage tenants.

Whether Cricklade was as significant, or as populous, in the early post-Conquest period as before 1066 is less clear. It never acquired the chartered liberties that could have made it self-governing, though a twelfth-century grant to the burgesses of freedom from toll, along with the construction of the town bridge before 1225, and establishment around the 1220s of a small hospital to support travellers and infirm priests, all may reflect the growth of commerce, which would include local merchants involved in the export of wool and import of goods from Flanders. There is no market licence, but then we need not expect one for so ancient a town; later evidence suggests it a Saturday event. Royal licence for a September fair – the timing not influenced by the parish church dedication – was obtained in 1257 by Baldwin de Redvers, alias de Insula, Earl of Devon and lord of the Isle of Wight, descendant of a probable companion of the Conqueror. This could point to an effort to help revitalize the economy; the fair is evidenced again in mid-fifteenth century, though where it was held, if not the High Street marketplace, is unknown, for there is no medieval evidence to associate it with Horsefair Lane, whose position rather suggests it a back lane to the eastern side of the High Street.

This Baldwin was grandson of an earlier man of the same name and Isabel, an heiress of the Fitz-Gerold family, which had previously held Cricklade manor and borough as a reward for service as chamberlain of the Exchequer; it appears to have been during that family's tenure that a bridge was built over the Thames at Cricklade. Cricklade was one of the manors she granted to Adam de Stratton, perhaps with a view to him, acting as her attorney, improving its value; he is subsequently seen buying up burgage rents in the town, but in 1289 they were seized into the king's hand after Adam was accused of corruption. For the rest of the Middle Ages Cricklade was usually assigned to one or other member of the royal family. However, in 1371 the borough was under the lordship of Sir Robert Knolles, though perhaps only with a life interest, for the king held the reversion.

Baldwin de Redvers' ancestors had risen in the world by supporting claims to the thronem first by Henry I and then by Matilda; their estates were particularly in the south-west and included several villages that would become towns and/or have market licences. Baldwin himself was particularly active in that regard. 1257 was a busy year for Baldwin de Redvers, or at least for the stewards of his estates. Having just reached the age of majority and about to come into the estates of his earldom, he sought to improve a number of them. On the same occasion that he obtained the fair for Cricklade (12 June), he did the same for his manor of Carisbrooke (Hants.) and for the boroughs of Highworth (Wilts.) and Lymington (Hants.), while for his manor of Stratton St. Margaret (Wilts.) he took out a licence both for fair and market. On 28 December of that year another burst of activity saw him obtaining grant of both market and fair for three Devon manors (Kilmington, Sutton, and Tiverton), as well as fairs for his manor of Topsham (Devon), the Devon borough of Honiton, and the Hampshire borough of Christchurch. Most of these properties had been held by his ancestors or predecessors as earls of Devon, so Baldwin was simply developing them, and in no instance did he engage in new town foundation. Dying prematurely of some epidemic while accompanying the king on an expedition to France, and predeceased by his only child, he was succeeded by his sister, the aforementioned Isabel, Countess of Aumale.

The regularity of the property plots along both sides of the High Street may be a feature of the original burh layout; the distribution of Cricklade burgesses (i.e. holders of plots within the burh) across northern Wiltshire at the time of Domesday is likely indicative of the kind of arrangements made for maintaining the burh defences. On the other hand, it could evidence a reorganization of tenemental structure along burgage lines at some later point – conceivably during Fitz-Gerold or Redvers tenure; this would have intruded on the large space posited as the Saxon marketplace, possibly as a unit of planned development more than the gradual ad hoc encroachment that typically reduced marketplaces, although the author of the Extensive Urban Survey report [p.16] posits some indication of infill at one corner of the crossroads. It seems likely that market activity refocused around the central crossroads and along the High Street arms of the crossroads, particularly that north of the crossroads; a fourteenth-century stone cross marking the marketplace stood in the High Street before being removed, in the nineteenth century, to the churchyard. By the fourteenth century a new parish had been carved out in the northern part of the town, served by what had probably earlier been a chapel situated very near the north gate through the burh defences (and possibly existing from that period) but rebuilt as a church in the twelfth century; this could point to population growth along the northern end of the High Street and into a suburb between the north gate and the river.

An incomplete extent taken of the manor of Cricklade in 1263, part of the inquisition post mortem on Baldwin de Insula (d. 1262), itemizes 28 burgages, 3 shops or workshops, and various undeveloped plots of land. If we may judge from their surnames, the tenants included a smith (who held two burgages and a workshop), a goldsmith, a fuller (a second fuller being a member of the jury that made the extent), two dyers (one also holding a plot of land, where he perhaps carried out his occupational activities), a mercer, the widow of another mercer, a butcher (who held only two plots of land), and one Alice Pedele who may have been a huckster. In addition there is a list of at least 21 men who paid the customary rate of 5d. a year as chepingavel; it would be tempting to look upon this as a rent for space in the market, but a jury of senior Cirencester burgesses in 1209 defined it as a licence for a resident to trade in the market without any liability for tolls, which may or may not have similar implications to stallage; among these licensees are a skinner and one of the dyers who was also a burgage tenant. The burgage rents, which varied probably according to the size of the tenement, look like those established in the post-Conquest period rather than the relatively low rents recorded by Domesday for older boroughs. Although there is no indication that cloth manufacture was very extensive, the townsmen included fullers and dyers in the late thirteenth century, and a century later weavers and glovers are evidenced in the town, along with bakers, brewers, and butchers, the last numerous enough that we hear, in 1442/3, of a shambles.

There is no sign of further expansion in Cricklade in the Late Middle Ages, nor in the Early Modern period, which suggests the local economy did not undergo any great developments and that the market remained significant only within the immediately surrounding region. Market tolls were generating little by mid-fifteenth century, and by the close of the century, and early in the next, were said to be worth nothing (as too were the fair tolls) – which may mean that efforts to collect the meagre income had ceased, although some trading in the marketplace may well have continued and even improved, for in 1663 the manorial lord acquired a new grant for a Saturday market, which also acknowledged that locals were exempt from tolls and stallage, and he erected a market house within the northern stretch of the High Street around the same time.