By 1086 Chelmsford was a manor held by the Bishop of London and remained under that lordship throughout the Middle Ages. Chelmsford is focused around the confluence of several rivers: the Can enters Chelmsford from the west, shortly after being joined by the River Wid, near Writtle, which lies just west of Chelmsford, and then joins the Chelmer (coming from the north) to the east of Chelmsford; the combined flow then proceeds eastwards to Maldon where it enters the wide River Blackwater whose estuary opens onto the North Sea. The Chelmer was navigable as far as Chelmsford for small vessels, but its surrounds were somewhat marshy, so that the town was almost surrounded by water-meadow. Positioned about half-way between London and Colchester, and on the Roman road connecting them, Chelmsford also had, in the Middle Ages, road connections to the port at Maldon, into the heart of East Anglia, south to the Thames crossing at Tilbury, and west to Bishops Stortford (Herts.), developed (probably a little later than Chelmsford) as a market town by the bishops of London. Chelmsford's position thus made it something of a communications hub fairly centrally placed within the county.

Chelmsford is one of the few English towns (as opposed to cities) that could claim to have had a market as far back as Roman times; its Roman name of Caesaromagus may actually be a reference to a market there, although there are several places in the area that claim to have been the site of Caesaromagus. This Roman market town – for which there is no reason to imagine continuity into the Early Middle Ages, though Saxons settled in the vicinity – was not quite on the same ground as medieval Chelmsford but south of it, along the London-Colchester road, and on the south bank of the Can; by 1086 its site had become the small hamlet of Moulsham, which would in the thirteenth century be effectively a suburb of Chelmsford, despite being on a separate demesne belonging to the Abbot of Westminster – until after the Dissolution both areas were united under the manorial lordship of the Mildmays. The ford by which the road crossed the Can had become impassable during the Saxon period and, after the Roman bridges decayed and collapsed, traffic diverted instead to a crossing at Widford, routing it through nearby Writtle, which became the prominent market centre of the area – at the time of Domesday much larger in size and population than tiny Chelmsford (which was even smaller than Moulsham) and generating twelve times as much revenue.

The gradual reversal of this situation began thanks to an initiative of Bishop Maurice (1085-1107) who, according to Camden – probably recording a credible local tradition – around the opening years of the twelfth century built a wooden bridge across the Can. This, in combination with Ceolmaer's Ford – itself provided by 1238, and perhaps much earlier, with two bridges (due to a division of the river into two arms) connected by a causeway – enabled the old route of the Roman road to be restored to use, rediverting traffic away from Writtle back to Chelmsford. These bridges would mark the southern and eastern limits of the medieval town. But even before the bridges were built, the ford, named for some Saxon settler, had become well enough known to give its name to Chelmsford hundred and to the river Chelmer. The importance of the Chelmsford crossing – a feature for which, it appears, the town was widely known – to the economy of the place was sufficient that when the Can bridge, over time, fell into dangerous disrepair, the Abbot of Westminster, probably working in conjunction with the Bishop of London, in about 1370 contracted with no less an architect than Henry Yevele, first to consult on the problem and then to oversee a rebuild in stone.

It was not until the far end of the twelfth century that Bishop William de Sanctæ Mariæ Ecclesia founded a town in his manor (known by the fifteenth century as Bishop's Hall), on a slightly elevated stretch of land between the Can and Chelmer, around what would become the High Street of Chelmsford; a map of 1591 shows the town stretching north-west from the Can bridge and with a marketplace in the shape of a funnel, or elongated triangle, ascending a slope up from the junction with what is now Springfield Road northwards to an open space in front of the church, erected on the highest point of the site; the Springfield Road turned north-east off the High Street to cross the Chelmer bridge and continue, past the manor of Springfield, to Colchester. This marketplace was probably created deliberately, by widening the road to the bridge, though perhaps not until many decades after the bridge had been built. From the north-east corner of the marketplace a narrower road ran along the east side of the churchyard and continued northwards, while from its north-west corner a second road (sometime Brochole, now Duke, Street) headed north-westwards towards Writtle and Braintree; neither of these attracted heavy settlement in the medieval period, except near their junctions with the marketplace.

Bishop William evidently had clear ideas on how he wanted to improve the financial viability of the estates belonging to his See, for within little more than a year after his election (1198), his officials had laid out burgage plots at both Braintree and Chelmsford, and the king gave his official approval to the project in 1200, his clerks issuing separate documents for each location (although the record of the transaction in the Charter Roll combined the two grants). Based on limited archaeological excavations, we know that some plots were laid out with a standard frontage of 2.5 perches, although documentary evidence suggests that larger plots may also have been provided; these plots stretched back a long distance, in the typical burgage style, with the rear boundary of each row of plots marked by a ditch. A manorial rental of 1428 indicates that burgage rents were set at 12d. a year, although some tenants were being charged multiples of this, presumably based on size of plot or on tenancy of multiple adjacent plots, amalgamated, the latter phenomenon confirmed by archaeology in Chelmsford's High Street.

In June 1199 the new king had issued to the new bishop royal confirmation of the bishopric of London's estates and chartered liberties, privileges, and exemptions, the last now including freedom for the bishop and his men from tolls throughout the realm. In September 1199 – almost eight months prior to royal approval of the town foundation – Bishop William proceeded to obtain a market grant from King John; it is worth quoting from the grant, as an example of one preceding the development of a standard formula for market licences, and lacking the clause making the new market conditional upon it not being detrimental to existing ones in the vicinity (which may have removed any recourse to Writtle):

"Know that we, for the health of our soul, the soul of our father, King Henry, and for the souls of all our predecessors and successors, have given, granted, and by this present charter confirmed to God and the church of St. Paul's, London, and to William, bishop of that church and his successors, that they may have in perpetuity a market at Chelmsford in Essex, in that part of the vill which belongs to his manor of Chelmsford, on one day per week – that is, on Fridays – each week of the year, together with tolls, stallage, and all other customs and liberties pertaining to markets." [T. Duffus Hardy, ed. Rotuli Chartarum in Turri Londinensi asservati, London, 1837, vol.1, p.17; my translation]

Hilda Grieve [The Sleepers and the Shadows. Chelmsford: a town, its people and its past, Essex Record Office Publication no. 100, vol.1 (1988), p.7] suggested that Bishop William's founding of market towns was prompted by a particular need for money to finance the ongoing building of St. Paul's cathedral, which would not be completed until 1240. This can only be a partial explanation, for leading ecclesiastics all over the country were engaged in establishing markets and new towns; such initiatives to develop the potential of their estates seem primarily intended to boost the revenues of their religious houses or dioceses in general, rather than driven by any stated financial need or theological rationale, beyond enrichment of the Church. Domesday Chelmsford may not have seemed an obvious money-maker, with only a tiny population and no prospect of much of a market developing organically there; but it offered the bishops a stop-over base in that area of their diocese, and one which might be better supplied by restoring the route carrying London-Colchester trade and encouraging use of the site for collecting and redistributing produce of farms in the area.

The establishment of an urban component within an area of light agricultural settlement would have stimulated growth in local population and in the breadth of any commerce that would be fostered there by a market alone. That some commerce was taking place is indicated by the presence in 1198 of at least three residents who could be amerced for infringing the assize of wine. The development of this wine trade at Chelmsford is evidenced by references in property transactions: in 1255 when Thomas Vinetar was acquiring a small piece of land at Chelmsford; in 1276 when Gilbert le Vyneter of Chelmsford was dealing with property rights of his wife Quena in Springfield and Writtle and Henry le Vyneter of Chelmsford and his wife Joan disposed of her property in Hadleigh; and in 1288 when we hear of William le Vineter of Chelmsford, who had at some earlier date been the owner of the land changing hands (pasture lying next to the road between Chelmsford and the marketplace at Writtle). Gilbert the vintner was almost certainly the Gilbert le Taverner whose wife Queniva, or Quenilda, had, ca. 1279, donated land in Little Baddow to Leigh's Priory, and who in 1285, as a widow, disposed of much of her late husband's property in Chelmsford and Springfield to a member of the Wendover family, which would come to own much real estate in Chelmsford. Gilbert had built up his holdings around the commercially strategic junction of streets close to the Can and Chelmer bridges; his tavern there would later be developed into one of the largest of Chelmsford's inns. These were not the only vintners evidenced in thirteenth century Chelmsford; among the few residents whose by-names, at the time of the national taxation of 1327, suggest occupations, those dealing in wine (vintners and taverners) are the most numerous. Whether they were directly involved in importing or just acting as middlemen between London importers and local consumers is harder to say, but the high number of wine dealers at Chelmsford, relative to the geographical size of the town, is an indication both of its role as a wholesale distribution point within Essex and as a pit-stop for travellers needing refreshment or overnight accommodations.

With an important inter-city road restored to a route through Chelmsford, it had remained to Bishop William to formalize and capitalize on a consequent growth in commerce by capturing tolls on the same, as well as steady rents from new settlers. He must have been satisfied by the results of his investment. The existence of the Chelmsford market is confirmed by a reference to it in 1205, in a recorded grant of one of the 'new plots' (on which a prior owner had already built) in the 'new market'. That it was attracting commerce is suggested by Bishop William, taking advantage of the king being an overnight guest of the manor in March 1201, purchasing (for 2 palfreys) a four-day fair to be held at the beginning of May; unlike the market grant, the fair grant included a clause making it provisional upon not being detrimental to existing fairs of the area, though no challenge to it is known. These formal grants meant that the market and fair were protected from quo warranto proceedings, which instead ca.1302 focused on Bishop Gravesend's right to view of frankpledge, exercise of criminal jurisdiction, and the assizes of bread and ale; a few years later a new bishop found it advisable to obtain royal confirmation of view of frankpledge at Chelmsford.

The new town of Chelmsford seems to have demonstrated the advantages of its position in the communication network quite quickly, in terms of attracting settlers – even though not all plots were taken up within the initial decade or so, and some were built on only when acquired to expand an adjacent holding. Names of property-holders at Chelmsford in the early thirteenth century suggest that – as at the new town established at Battle – a number were drawn from as far away as Normandy – perhaps thanks to Bishop William's connections there – or elsewhere in northern France.

That Chelmsford was also successful in capturing a share of regional commerce, and building commerce based on local industry, is seen from the allocation of particular parts of the marketplace according to types of goods – perhaps not until the fifteenth century, when this is conspicuous, but quite conceivably at earlier date. Grain was sold at the higher, north end, near the market cross, in an area that became known as Cornhill; groupings of stalls for leather goods, fish, and poultry were towards the southern end. Workshops of farriers and smiths were situated even further south, sensibly positioned between the Can and Chelmer bridges, so as to be convenient for through-traffic. Six butchers' stalls are recorded as being set up outside John Gybon's inn near the Can bridge – again a convenient location, in terms of disposal of blood and offal if animals were slaughtered there – and this may have been the medieval shambles; in the sixteenth century we hear of a 'new shambles' of six butchers' shops established within Middle Row (see below). Yet the earlier location may just have been a group of illicit stalls, for the manorial court in 1387 challenged Gybon's right to erect them. In fact a number of questionable stalls appeared in the years following the destruction of manor records by the rebels of 1381, and it took years of court hearings to sort matters out; the investigations show that some of the more prosperous townsmen held multiple stalls, some of which they must have been renting out to other tradesmen. Some stalls were in front of townsmen's houses; in the fifteenth century we see more holders of those tenements facing onto the marketplace being allowed to rent space in front of their houses for setting up stalls. By 1428 rents from stall pitches amounted to about 10s. in manorial income, at an average rent of 4d., but this did not include holdings that had been converted to shops. According to a local by-law written down in 1382, but almost certainly of earlier date, stalls had to be removed from the High Street after each market session closed; this is standard procedure for many outdoor markets today and probably those of the Middle Ages, but it is seldom we find the requirement recorded. Yet already by that date some market vendors were acquiring from the bishop a firmer title to small plots within the marketplace on which they could erect more permanent structures, in the form of shops, in return for an annual rent of a few pence. Another indication of growing commerce comes from the presence of the king's purveyors of supplies at Chelmsford's market, which prompted complaints of abuses at the hundredal enquiries of 1274, and by the fining in 1292 of nine men for forestalling goods in order to drive up market prices.

The parish church of St. Mary was at the northern end of the High Street, behind a wide open area which can be considered the core of the marketplace. The church was built in the early thirteenth century – probably close to the date of the town's foundation – though largely rebuilt over the course of the fifteenth. A tollhouse, serving for market administration and manorial court, faced onto the market from the south side of the churchyard. A little further south stood the market cross, which came to be mounted atop an open-sided building that hosted part of the grain market and, periodically, the shire court. For the central location of Chelmsford within Essex made it a useful base for county administration. Royal justices were holding their sessions there from the early years of the thirteenth century, and perhaps as early as 1184; from 1218 it became a regular seat for various assizes (including eyres), displacing not only Writtle in that role but even Colchester, and paving the way for later official recognition of Chelmsford as the county town, which did much to boost its fortunes. Important inquests were also held there, as also (from 1225) meetings of commissioners appointed to assess taxes on the county; Grieve [op.cit., p.14] concluded that by mid-thirteenth century Chelmsford had become "the place usually appointed for the transaction of 'the king's business' in the county." The judicial sessions and other administrative meetings drew to Chelmsford numerous participants from all across the region – most of them the more prosperous members of Essex society – who were likely to spend money at the town's inns, taverns, shops, and market; the Bohun earls of Essex had a staffed town-house there. In 1494 Chelmsford was designated the Essex town where would be kept the official standards of weights and measures, against which others in the county could be checked for accuracy.

The bishop's manor-house and mill were to the north of the town, the two areas being linked by a High Street continuation that became known (by 1386) as New Street; its south end saw some expansion of the residential area in the fourteenth century. However, the greater part of the area between the planted town and the manor-house was not settled, being vulnerable to flooding. Moulsham had a chapel by 1157, but remained part of the parish of Chelmsford. The Dominicans had established a friary in the area between Moulsham and Chelmsford by 1277 and a leper hospital existed by 1293 rather further south along Moulsham Street, beyond the inhabited area. Moulsham must have benefited from the traffic, commercial and otherwise, drawn through Chelmsford and its population had likewise grown, so by the time of the poll tax of 1377 that population was about 75‰ the size of Chelmsford's. The southern part of Moulsham Street, between friary and hospital, saw an expansion of urban settlement from the late fifteenth century; at some point prior to the 1591 survey, a market-cross was installed on the Moulsham side of the Can bridge and butchers and farmers sold victuals there, but this never become a formal, licensed market. Otherwise, Chelmsford town's size and layout expanded little from its original form, population growth during the Late Middle Ages and Early Modern period being accommodated as mentioned above, through reclamation of marshy land by the riverside (particularly along approaches to the bridges), and by licensed infilling of the centre of the broader end of the marketplace.

That infilling, which seems to have begun in the second half of the fourteenth century, eventually gave rise to separate streets – High Street and Back, now Tindal, Street – on either side of two blocks of buildings, kept separate by a short intervening lane. One block was known as Middle Row or the Shoprow (a name first encountered in 1384); this island of permanent structures was not limited to shops, as we understand the term, but also included at least one eatery, as well as residential components, mostly as solars added atop shops. The other block, Little Middle Row, probably represents an extension of the infilling trend, slightly further south, in the fifteenth century and may have prompted some reorganization of the marketplace. Even in the leathermarket, an area immediately south of Little Middle Row, the old custom of dismantlable stalls was being compromised, as exemplified by the case of John Yon, a glover who held three stalls here and who in 1416 was licensed not only to increase his retail space with a fourth stall (of about 3 feet by 3.5 feet), but to erect a pentice to cover his row of stalls, at of course an increase in his annual rent.

Though some tenants acquired additional small plots to develop their properties in the two blocks, expansion was limited by the existence (by 1384) of a watercourse that ran through the marketplace just west of the blocks. It was fuelled from a spring to the north of the town, the water brought through underground pipes to a conduit near the north-west corner of the marketplace, where townspeople could obtain fresh water before the residue was fed into a ditch that provided drainage for market vendors and householders; further south it was diverted to empty into a canal connecting the Can and Chelmer rivers. Grieve [op.cit., p.55] suspected, quite reasonably, that this sanitation system may have been the product of a collaboration with the Dominicans, who in 1341 had laid pipes from the same spring to bring clean water to their friary – a project to which several Chelmsford residents (John Baldewyne chandler, Joan the widow of William le Vineter, and John le Smyth) had contributed through donations of land. At earlier date the town midden was situated within the widest part of the market, which can hardly have been appetizing, so the drainage channel alleviated one sanitary concern, even though it contributed to polluting the river.

Even though marketplace frontage may have been in demand, most tenement plots in the town did not become very densely built up during the fourteenth century. Poll tax evidence indicates that by 1377 the population of Chelmsford was still considerably smaller than that of Writtle, although that is attributable primarily to Writtle's much larger territory. The fifteenth century, however, saw any vacant plots taken up, some High Street tenements divided into two or more residential units, passageways between tenements built over, houses growing vertically as upper storeys were added, and more stalls and shops being established in front of homes, while infilling of the marketplace continued apace, and even part of the churchyard was taken over by cottages. Although recorded taxation and other figures cannot necessarily be taken at face value, the impression given is that over the course of the fifteenth century the population of Chelmsford may have doubled, as expanding commerce and industry and urban opportunities continued to attract migrants away from the countryside.

Grieve's identification of occupations documented in Chelmsford during the reign of Edward III shows the kind of range we would expect in a medium-sized market town. Food services are represented by cooks, innkeepers, taverners, fishmongers, butchers and bakers; the cloth and leather industries by fullers, dyers, tailors, blanket-makers, tanners, glovers, and shoemakers, while other manufacturing and the building trades by smiths, an arrowsmith, a bowyer, ropemakers, carpenters, tilers, and masons; the middleman sector by vintners, spicers, woolmongers, skinners, a chapman, and the Elias the Chandler who in 1323 was tenant of one of two burgage plots on the High Street (now nos. 63-66) excavated in the 1970s – the other plot holding an inn owned by John Wymond around mid-century. The cloth trade is further evidenced by the case of a London man outlawed ca.1376 for having stolen three packs of woollen cloth from Geoffrey Taillour of Chelmsford, William Webbe (i.e. weaver), and William Hosiere; though whether this cloth was manufactured in Chelmsford or being taken there for sale is not specified.

By contrast with the various artisans and small-scale or specialized traders, mercers or general merchants are less in evidence at Chelmsford than one might expect, however. A large proportion of Chelmsford men recorded as involved in property transactions during the late thirteenth and early fourteenth centuries had occupational by-names or surnames, a reflection of the commercial character of the urban community there; this remains somewhat pronounced in the latter half of the century, though such names are by then less reliable indicators of actual occupation (as John Wright of Chelmsford, described in 1387 as a chandler, illustrates). It is also from the early fourteenth century that we hear of shops existing in the town; in 1324, for example, John le Cook of Totham acquired one in Chelmsford from the son of Roger le Deghere (i.e. dyer) and later that year a second from William le Arwesmyth, while sixty years later Nicholas Cook of Chelmsford sold a messuage and three shops to fellow townsman Robert Glovere. That these were structures more permanent than stalls is shown by the fact they were treated as real estate that could be bought and sold, not only by local men but also by outsiders, notably Londoners, who were probably interested in them as investments and sources of rents, rather than as branch outlets for their own businesses.

The manorial survey of 1591 claimed that Chelmsford had sometimes been referred to as a borough. Manorial records of the thirteenth century do distinguish between the burgus of the vill and the vill's uplands, where dwelt and worked the unfree tenants; in 1262 there is mention of the burgesses of Chelmsford, and by this date part of the land bordering the river was known as 'Townsmen's Meadow. But it was not a chartered, self-governing borough; in line with the usual ecclesiastical conservatism, the bishops kept the townsmen on a short leash. It was administered by a resident bailiff, who was at least a local man, with the manor court presided over by a non-resident steward, both episcopal officials; it was the former, or some subordinate, who collected market tolls and stallage, and who was the target of a complaint in 1280 by the Archbishop of Canterbury to the Bishop of London that tolls had been demanded from his tenants trading at or passing through Chelmsford, despite the archbishopric's nationwide exemption from toll, and goods seized when his tenants refused to pay. The shoe was on the other foot in 1311 when the Bishop of London, claiming similar exemption (on the grounds of John's charter of 1199), obtained a writ forbidding Colchester officials to demand toll of his tenants. It is hardly surprising that toll-collectors were reluctant to accept claims of exemption without solid proof. With the growing number of exemptions granted by kings and other lords, market tolls were a diminishing revenue over the course of the Late Middle Ages. An account of the Chelmsford bailiff survives from 1318, though covers only a portion of the year; it reported 19d in market tolls over a seven-week period which, if reasonably representative, would indicate an annual income of perhaps 12s. – not a very high amount, and probably paid largely by farmers of the region. Rents and punitive court fines, by contrast, were far more lucrative, although we have to remember that it was commercial activity that generated many of the disputes or offences leading to fines, and that provided family incomes enabling rents to be paid.

A pair of by-laws of 1382 are recorded on the initial membrane of a manorial court roll covering a span of years, and suggest some local voice in local administration; although said to be enacted by the common assent of all the burgesses, this was perhaps given only through the jury of capital pledges who acted as the voice of theChelmsford community in the leet court. These by-laws must have come into existence at an earlier time, but record of them – if they were not preserved simply in the memories of the leading townsmen – was likely destroyed in the uprising of 1381. A gild of Corpus Christi, in existence by the late fourteenth century, appears by the early sixteenth to have become (if it was not earlier) a corporate expression of mercantile interests in the town, though in the fourteenth it, like the gild of Holy Trinity, revealed only its socio-religious aspect in surviving records.

Despite its importance in county administration, Chelmsford did not rise into the mainstream of English boroughs, and after sending representatives to a parliament of 1337, it quickly begged off being required to do so in future, on the grounds it could not support the burden of parliamentary wages, though it may have been more a case of the bishop not wishing his burgess tenants a forum in which they could express ambitions or be infected by the aspirations of other towns. Chelmsford did not formally acquire chartered borough status until 1888 nor did it expand greatly before mid-nineteenth century. Yet it continued to prosper, as market town and county town, in the post-medieval period, its weekly market continuing on Fridays. The 1591 survey could boast that the town comprised "more than three hundred habitations, divers of them seemly for gentlemen, many fair inns, and the residue of the same habitations for victuallers and artificers of city-like buildings, and are all holden of the said manor of Chelmsford, mediately, or immediately, by reasonable rents, customs, and services." [quoted in Thomas Wright, The History and Topography of the County of Essex, vol.1, London, 1831, p.84].

The bishop surrendered the manor to the Crown in 1545, and in 1563 it was purchased by Thomas Mildmay junior (ca. 1510-66), who had earlier acquired Moulsham manor and the former Dominican property. His father, Thomas Mildmay senior (ca. 1490-1550), had established the family's prominence through commerce, being described in 1530 as a mercer when leasing a tenement with stalls from the Corpus Christi gild; three years earlier he had acquired another house in Chelmsford, considered the finest in the town, from Richard Rich, later Chancellor of the Court of Augmentations to Henry VIII and himself of a London mercer's family. It was through Rich that Thomas junior obtained a bureaucratic post as auditor, and Thomas' younger brother Walter (a future Chancellor of the Exchequer) as a royal surveyor; his office involved Thomas in the Dissolution, giving him advantageous access to properties transferred to the Crown. He went on to represent various Cornish towns (he being an auditor for the duchy of Cornwall) in parliament and to be appointed a sheriff of Essex, as did his own son, yet another Thomas, who, having been knighted and married to a daughter and heiress of the Earl of Sussex, commissioned a survey and map of Chelmsford manor and town in 1591. The Mildmays exemplify that the commerce of Chelmsford, although only a medium-size market town, could produce men of some wealth and rising status.

Yet, even before the 1545 surrender, episcopal interest in manorial administration was waning; for, in the late fourteenth century the practice of using villein labour to cultivate demesne lands was giving way to putting them out to farm, in order to obtain a more stable and predictable income. This practice continued, with minor variations, beyond the close of the Middle Ages. In 1514, Bishop Richard FitzJames leased the manor for nineteen years to John Markdaye, a Chelmsford yeoman. For the sum of £40 annually Markdaye thereby came into possession of the manor-house, tollhouse, a riverside mill and storehouse, barns, fields, and livestock, and the responsibility to maintain them. But the profits from fairs and markets, along with other major sources of income from the town – possibly rents and court revenues, though apparently not the assize of bread (as Markdaye was assigned the weights) – the bishop reserved to himself.