There were two settlement foci in the Billericay area in the Late Iron Age and Roman period, one to the north of the town and one to the south under the present Billericay School. The settlement to the south appears to be urban in character.
The settlement probably originated as a ditched enclosure of Late Iron Age date and grew into a small town, covering an area of approximately 8 hectares, in the Roman period. It appears to have been centred on the point where the east-west Roman road crossed the ridge. Cremation burials were found throughout the area, with the main cemetery focus around the edges of the settlement, to the east, north-east and south. Those to the north-east at Windmill Hill are reported (Hull, 1963) as being grouped in threes or fours, suggesting family groupings within the cemetery itself, the cemetery to the south may have been enclosed. There are antiquarian reports of two possible masonry structures, one with a cement floor and one with a hypocaust, in the northern half of the settlement. Other features include post-holes, gullies, ditches and gravel spreads, and it is probable that some of these at least represent timber dwellings. Two, possibly three, pottery kilns and two corn-dryers have been found, providing some evidence for the local economy.
To date there is no evidence for occupation of the area during the Saxon period and the area may have been marginal land.
Medieval Billericay was a thirteenth century creation of the monks of Stratford Langthorne Abbey. The name itself is not recorded until 1291, although there may well have been a market on the site since 1253. Billericay was built on waste-land, where the Mountnessing and Great Burstead parish boundaries met and incorporated several manors. In 1345 a chapel was built in Billericay, subsequently the area belonging to Mountnessing parish within the town was transferred to Great Burstead parish so that the Mountnessing parishioners could attend the chapel.
The parochial division down the High Street between Mountnessing and Great Burstead parishes helps explain the town’s medieval topography. The town occupied the area between the junction of Western road and Norsey Road with the High Street and the curve in the High Street opposite the Red Lion Inn. Two distinct morphological units can be identified; the eastern High Street/Chapel Street block and the western High Street/ Western Road block. In 1983 (Eddy and Petchey) it was thought that the eastern unit was probably earlier, representing the original settlement associated with the market of 1253, and that the western side (Mountnessing parish) was a later development. It is now suggested on the basis of the Listed Building evidence that the opposite is the case. The town is typical of the type of medieval new town that grew in an organic manner due to the stimulus of trade, rather than because of official patronage. The current interpretation of the morphological development of Billericay is very similar to that present in Great Dunmow.
The post-medieval town expanded in the form of ribbon development along the existing medieval street structure. It was not until the 20th century that the town took its present form.
Fieldwork undertaken within the medieval town has largely proved disappointing, principally because the areas of development has led to a concentration of archaeological investigation on the backlands area rather than the street frontage. Some areas also appear to have suffered considerable disturbance from gravel and brickearth quarrying.