Saxon Hamwic was an undefended settlement. After its residents relocated in the tenth century to a new site, which would develop into Southampton, a defensive ditch was dug, at least on the shoreward site; this suggests that Viking raids of the period may have been one of the reasons for the relocation. Defences and defenders were not, however, sufficient to prevent the "new town" being plundered by Danish forces several times during the early eleventh century. After the Conquest, Southampton grew into a leading south coast port, used both for import/export and for the transit of royal forces, and later served as a base for naval construction.

The introduction of a Norman castle (first mentioned in 1153) did not provide the protection the townsmen felt their families, homes and businesses needed, and from the late twelfth century a half-hearted effort was underway to improve the town's defences, although whether prompted by the civil war of preceding decades or a desire to control trade routes into the town, we cannot say. The first step (ca. 1175) seems to have been to reinforce an existing wooden gate, on the east side of town, with a stone arch; the Eastgate was joined by a new gate at the northern entrance to the town: the earliest version of the Bargate (1190) was a simple structure, although later development made it larger and more elaborate. In the opening years of the next century a ditch was dug and an earthen rampart thrown up between the two gates; it was extended in subsequent decades to define the entire northern and eastern boundaries of the area of heaviest settlement, terminating not far from the castle. In both 1202 and 1203 King John, who had a small fleet to protect in Southampton's harbour, allowed the town to deduct £100 from its fee farm for application towards the cost of enclosing the town; we can guess this helped finance the rampart and ditch, but there is no indication that wall-building was underway at that period. Murage grants were obtained for much of the period from the beginning of the 1260s (when the Montfortian and royalist factions were moving towards civil war) to the end of the'80s; if this money was spent as authorized, the earliest phase of adding a stone wall atop the northern ramparts, and perhaps the eastern as well, may have been the result.

The sides facing the water (sea to the south and river to the west) were not yet protected, although from 1299 there was work on building a proper quay incorporating some kind of enclosure. But there must have been concern that fortifications would impede public access to the harbour on which Southampton's prosperity depended; reluctant to erect solid defences there, the borough authorities (many of whose members held property along the waterfront) gambled on English sea-power to keep the Channel free of enemies. Yet this was precisely the direction from which danger was most likely to come. In 1319 there was fighting between townsmen and crews of Venetian galleys harbouring at Southampton; and in 1321 a Winchelsea fleet, as part of a campaign to assert Cinque Ports dominance along the south coast, landed at Southampton and burned a number of ships beached there. The risks increased once England and France were at war. The 1320s saw an effort to continue work on fortifications, aided by royal orders and grants of murage and quayage; but although gates and bars protected access to streets running from the southern and western edges of town, and a barbican was put up on the seaward side, the defences were still inadequate. Meanwhile, the king's castle had been allowed to fall into disrepair.

Graphic demonstration of the weak defences came in October 1338, when a fleet of French and Genoese ships descended on Southampton early one morning. There is no indication the townsmen were able to mount any serious resistance. Many of them were slain or carried off for ransom, and their properties and merchandize plundered or destroyed by fire. No help came from county forces supposed to be guarding the coast. After the raiders had withdrawn, local and county men, it was later accused, had themselves looted wool and wines belonging to the king or to foreign merchants stored in Southampton. Large areas across the town, but particularly in the southern half, were burned down (probably including the house of the mayor of that year, where the town treasury and archives may have been kept) or were so badly damaged they had to be demolished; and during the coming year mercantile commerce came to a virtual standstill.

Local government would likely have been disrupted, many of the town rulers having lost their lives or their homes, but this problem became academic when a furious Edward III suspended the borough liberties and appointed his own custodians of its government, supported by a small garrison; their focus was on repairing damage to the castle. The king also appointed a commission of enquiry into the failure of the defensive system. The investigation incorporated a review of the performance of local officials and one, a former mayor and a customs collector, was briefly imprisoned in the Tower and saddled with a ruinous fine for customs fraud and misappropriation of money collected for construction of defences. In 1341 another investigation was held into the financial accounts related to the barbican.

1339 saw fears of yet another raid. The king increased the garrison size, assigned two pinnaces to the port to help with defence, supplied the defenders with ordnance, and even visited himself to consult on defensive arrangements. He was determined that the defensive circuit must be completed properly but quickly. County sheriffs were ordered to impress masons, carpenters and other workmen for the task and to bring in building materials. Local self-government was restored and some financial relief provided. The townsmen were instructed to rebuild their houses as best they could, and those who had abandoned the town were ordered to return. Activity was soon underway on repairs to existing defences, quarrying of stone for new construction, deepening the ditch, and constructing new springalds and a large mangonel. After the English naval victory at Sluys, fears of a French threat diminished, the garrison was withdrawn, and responsibility for work on the fortifications and for local defence was turned back to the townsmen, who for a while at least were more motivated to provide the town with what it needed.

The collection of murage was permitted again from 1345, being renewed periodically to cover much of the period into the 1380s; but with commerce at Southampton badly depressed, the income from murage during that period could not have met needs. An examination ordered by the king in 1353 of the state of the defences revealed problems: the rampart on the eastern boundary was eroding, and the wooden parapet of the walls there was weather-damaged; some of the newer walls had been constructed hastily and were not thick enough, their foundations were too weak, and the facing of poor quality. The king's response to a request for help was simply to renew the murage. A further examination, in the early 1360s, intended to see if murage was being spent to good effect on the defences, brought out more problems – such as buildings, gardens and orchards being situated adjacent to the defences, to the latter's detriment – and a series of recommendations that proved difficult to implement; the owners of properties alongside the walls and ditches naturally resisted their removal, as did the owners of houses facing the quayside, whose windows and doors were ordered blocked up. Ironically it was the integration of those merchants' houses into the defences that gave rise to innovative improvements. The blocked openings subsequently had keyhole loops inserted to serve hand-gunners (as well as archers or crossbowmen), making that western stretch of wall one of the earliest defences in the country known to incorporate gunports. And, since the walls of the stone houses were not thick enough to support a parapet, a second wall in the form of a series of arches was built against the former house-fronts; this provided for a parapet while incorporating concealed spaces (machicolations) through which defenders on the parapet could project missiles down at attackers who entered the recessed arches.

In 1369, shortly before the war with France became active again, the king authorized the town government to impose a tax on residents for improving the defences. Such a tax was again granted in 1376 and, between then and 1382, the town's fee farm was remitted for application to wall-building. During the early fifteenth century, the king provided for continuing work by granting an annual allowance from customs revenues, to supplement a partial remittance of the farm and an amount required to be raised from local sources (and, later, income from property the king allowed the corporation to acquire in mortmain); some of this work involved strengthening towers and gates, including the accommodation of guns. Maintenance and upgrades continued piecemeal throughout much of the century, fears of a Yorkist assault in 1460 reminding residents of the rationale for the endeavour. Despite subsidization from royal revenues, the financial burden on the town itself continued to be great.

The four decades following the French raid of 1338 were probably those of greatest activity in wall-building, with much of the western and southern stretches being erected; although the 1360s enquiry suggests that the fortifications facing the waterfront were cobbled together by incorporating private houses into the barrier, and the name of one of the properties on this route suggests that chains may have been used as an obstacle at some time. It was in the latter part of this period that we start to hear of the Westgate, which opened onto the western (riverside) section of quay, and of the south gate of the town, referred to in 1378 as the New Gate, and later as the Watergate.

The Watergate gave access from what was Southampton's high street, running through the town from the northern gate (Bargate), to the town quay; the section of quay near the Watergate, after redevelopment in 1410/11 (including construction of a crane there), became the principal point for the loading and unloading of ships. The building of the new quay is an example of a public work financed by a private citizen: Thomas Middleton. The gate provided a base for the water bailiff to collect local customs on imports and exports; his office was perhaps in one of the upper chambers. On the west side of the gate was the house were the king's customs were collected. Not far from the gate was the Weigh House, containing the beam used determine the weight of wool for purposes of customs assessment, and also the Wool House, built by Middleton as a strong warehouse for storing wool, and perhaps the finest (and only surviving) example of several such warehouses in medieval Southampton.

In their efforts to spread the burden of the cost in maintaining and upgrading town defences, by 1454 the Southampton authorities had allocated responsibility for stretches of the wall among the 400-plus properties in the four wards into which Southampton was then divided. As for the towers, those the authorities did not think better to keep directly under their control were assigned to individuals or religious houses, or – in the sixteenth century – to particular craft gilds, along with responsibility for defending them. This approach is first seen in regard to the tower associated with the Watergate, leased to a succession of townsmen during the fifteenth century:

• William Ravenston (1403-?);
• William Soper (1433-77), one of the leading citizens, who built or rebuilt a pair of towers beside the gateway (the greater being immediately west of the gate) in return for a long lease. Although Soper died ca.1459, he had already (since 1439) sub-leased to his legal advisor John Ingoldesby, who obtained licence to add one or more solars above the house; he surrendered his rights in the property in 1477.
• Roger Kelsale; (1483-?)
• and Richard Palshid (1496-ca.1534).

The first two lessees paid the nominal rent of a red rose, their financial obligations being primarily in improvements to the structure and its maintenance in a defensible state; the latter two paid the almost equally nominal sum of 12d. a year. In his lease, Soper was permitted to build a house on the east side of the gate, so long as it left an access route (13 feet wide and 16 high) through to the street that ran in front of the wall. In Soper's will this building was described as a shop with a (living) room above it; this was presumably the house inhabited by Margery Kyrton in 1481, and she was said still to be resident when Palshid took on the lease. His lease was framed much the same as Kelsale's, with the same rights and obligations, but the term was 84 years; it also mentions a portcullis (with which Palshid was not to meddle), but whether the portcullis was added during Kelsale's tenure cannot be said with certainty. The shed that Kelsale was permitted to erect, and that Palshid was allowed to keep, was a new requirement, doubtless stemming from Kelsale's business activities.

Kelsale's tenure of the tower and its appurtenances was not smooth sailing, however. He was one of four Southampton men attainted before the parliament of 11484 as rebels, implicated in the uprising of malcontents against Richard III that has been associated (questionably) with the Duke of Buckingham and Henry Tudor's abortive attempt to land at Poole. Of his fellow rebels, one is known to have held shops in Southampton, but later made Poole his base when he went into the customs service; two others were former mayors of Southampton. Of the ex-mayors, Walter William would have been mayor at the time of the uprising (October 1483), but with rumours of the event spreading in advance he had already thought it prudent to flee to sanctuary, and a replacement had been elected; the other, William Overey had served as town clerk before proceeding to political office and his clerical skills helped him to a post as customs controller.

Roger Kelsale himself was a yeoman of the crown throughout Edward IV's reign; tasks he performed for the king included the manufacture and transport of artillery, supervision of work to improve and maintain Southampton's walls and harbour, and the victualling of ships that were to pursue one of Richard III's Woodville enemies. Either his influence or the favour he found with the borough authorities at that period is reflected not only in the grant of the lease of the Watergate tower, and also, later that same year, of a 40-year lease on another house, but also in his selection to represent the town at the 1478 and 1483 parliaments. By 1476 he had also become a customs collector at Southampton, his term in that post being renewed in 1483. However, in the following year he and others (including Richard Wiskard) were being sued by the town to account for monies received from the king towards repair of the walls, but not turned over to the local authorities for application. His attainder and the associated order to seize Kelsale's property (a potential source of problems for the town, if the tower had been involved) cannot have done his reputation much good, although he was able to take advantage of the change of monarch to have the attainder reversed in 1485 and be reconfirmed in his post of customs collector. That he drew up his will in October 1485, however, suggests apprehension or declining health. Yet he may have survived a few more years, for Palshid's arrangement with the corporation in 1496 has less the look of a new negotiation than the assumption of the remaining term on Kelsale's lease.

Regardless of their politics, men such as these, taking on what Platt calls "repair leases" of public buildings, can be considered civic-minded; but to be so in the Middle Ages tended to involve combining the qualities of benefactor and entrepreneur. It need not surprise us that, in the case of the Watergate lease, such men were local administrators and/or lawyers, with strong interest and expertise in accumulating real estate; nor, given the location, that some were involved in the customs service. It is of rather more interest that some lessees were involved in administering work on the town defences or other efforts in support of military initiatives, but we cannot generalize from that: Southampton itself played an important role in coastal defence and as a staging-point for foreign expeditions; by contrast, at Oxford it was students and staff of the university who showed a high interest in renting residential space within the city fortifications.