One of a string of towns close to the border with Somerset, Westbury lay at the centre of one of the largest parishes in Wiltshire, ringed by a number of other settlements which, between them, would have provided a relatively large consumer and supplier base for Westbury's market; the parish was coterminous with Westbury Hundred. It lay on an ancient route between Chippenham and the south coast of Dorset and one along the northern edge of Salisbury Plain; the main street through the town, crossing the marketplace, connecting to Trowbridge and Warminster. Westbury was not on any large watercourse, but was served by a number of springs, mostly feeding the Biss Brook which ran into the river of the same name. The nearby Selwood forest was a source of food, fuel, forage for pigs, and building materials. The medieval settlement is not very well documented, nor has archaeology yet produced much that throws light on its development.
Despite the implications of Westbury's name, no evidence of a Saxon burh has been found there and 'bury' may refer to something else. Lack of evidence of any defensive fortifications, or even natural defences such as rivers or marshes, suggests settlement may have developed in the later Saxon period. The earliest mention of it is in Domesday, as a royal estate with a church that may have been a minster. Its population then included, in addition to a large number of mills (and presumably millers), potters, swineherds, and bee-keepers; these occupations are not commonly mentioned in Domesday Book and the VCH Wiltshire [vol.8, p. 165] suggests it "may indicate an exceptionally highly organized manorial economy." We cannot tell from Domesday whether these individuals were working in what later became the town. According to the hundred jurors of 1275, after partial dismantlement of the estate, Henry II had granted the remainder of the manor to Reginald de Pavely (ca.1173), whose son Walter de Pavely (d.1256), and Walter's son Reginald (d.1280), held it in their turn. The jurors did not know by what right Walter had held the hundred itself, which led to a court challenge from the Crown a few years later, arguing that the hundred had only been granted to Walter to hold at the king's pleasure; but the jurors on this occasion supported the hereditary claim of the family, which continued to hold property there into the early fifteenth century, although partitioned between female heirs from 1361.
Reginald II was followed by Walter II (d.1323), who served as county sheriff in 1289 and 1296. It was Walter I who obtained the first licence for Westbury, in 1252, for a Friday market and a November fair. Walter II acquired in 1291 the grant of a Tuesday market and July fair, although the latter was in 1297 shifted to May. In 1460 a third market day would be added, along with three more fairs in spring and autumn; by then the ownership of the earlier markets and fairs, as well as of the portmoot and other institutions of judicial jurisdiction, had been divided among the female heirs of John Pavely. The inquisition post mortem on John (1361) does not provide a valuation for the tolls from markets or fairs, but that on Walter II estimates them (under the hundred rather than the manor, even though the grants were for the manor) as 6s.8d from the market and 3s.4d from the November fair; why the May fair is ignored is unclear. At a re-partitioning of the inheritance in 1368 we hear of more than a dozen burgage rents in the borough, as well as a rent received from the 'shamelhouse' in the town of Westbury, which suggests a market house accommodating sellers of meat and/or fish, or perhaps a slaughter-house.
In 1540 Leland characterized Westbury's market as small, but it was doing a good business in grain and had not yet succumbed to competition from Warminster. Sheep and grain must long have been the principal focus of agriculture, while cloth manufacture had become, as in most Wiltshire towns, the dominant industry by the close of the Middle Ages. In 1433 one Westbury clothier, William Gaweyn was suing two mercantile members of the Crosse family of Lynn for a debt of £20, a deal perhaps transacted at a fair, though not necessarily that of Westbury. In 1459 William Athelam, a Westbury cloth-maker, sold 26 cloths for £99 to German merchants in London, while an aulnage account for half of 1466 shows him having paid subsidy on 62 cloths, and several other Westbury cloth-makers as having been even more productive.
The historic core of Westbury lies north-east of the present town centre and its High Street. The street called Market Place, although no longer used for that purpose, presumably marks the historic site of the market. South of it is the parish church, which is likely to be on the same site as the church mentioned in Domesday, though this was largely rebuilt in the Late Middle Ages. Church Street runs southwards from the church, but was probably not a Saxon route, for the Saxon manor-house and village are suspected to have been immediately north of the church and approached from the east by what is now Alfred Street and from the south by another ancient track which swung through the village and met the road from the east in the vicinity of Market Place, before then heading north again. If this conjecture by the (unidentified) author of the Extensive Urban Survey report is correct, it would suggest that Westbury's market site may date back to Saxon times. That the marketplace is now only a street is likely the result of post-medieval encroachment; the Survey report envisages a wider rectangular space in the mid-thirteenth century (though still relatively modest in size for an urban marketplace), immediately north of the churchyard and east of the Saxon village and manorial enclosure. By the fifteenth century settlement had spread out from the Saxon core in most directions: around both the eastern and southern approach roads to the marketplace as well as that heading north from the marketplace (to Trowbridge); immediately south of the church, along Church Street; and in a disconnected area at the south end of Church Street. Some of this spread may have been the result of late medieval population growth as Westbury's economy expanded through cloth-making, but we may suspect that burgages established around the time of the earliest market grant would have focused on the marketplace and the immediate stretches of roads accessing it from east, west, and (particularly) north.
It is not clear whether any of this spread of settlement represents the creation of a planned town. The presence within Westbury of lesser manors and minor estates before the time of the Pavely lordship could have complicated any such initiative, except perhaps in the vicinity of the marketplace and to its north. The evidence for the layout of pre- and post-Conquest Westbury is slim and any reconstruction of it based partly on topographical indicators. Identifying the features of medieval Westbury is complicated by the fact that the town and what was technically the borough were not one and the same, at least by the eighteenth century; the 'borough' referred to a collection of burgages distributed through the town, but focusing in three enclaves: around the Market Place and streets leading out of it, the neighbourhood of Eden Vale (west of the modern town centre), and a location called The Knoll at the southern end of Church Street. Some of this fragmentation of the borough may be attributable to post-medieval circumstances, when burgage-owners were those eligible to vote for parliamentary representatives. The portmoot was explicitly stated in 1443 as being an institution of the borough, yet institutions typical of late medieval self-governing boroughs, such as mayor and council, are not in evidence; medieval administration and revenues evidently remained in seigneurial hands. The minor status of Westbury as a borough is indicated by the fact it was not instructed to send representatives to parliament until 1448, although attendance thereafter was regular, perhaps a reflection of economic and population growth.