The first of these two documents was part of a patchy compilation of national laws and civic customs and liberties, pulled together around 1215, perhaps to serve a fledgling local administration now headed by a mayor and facing a role in the constitutional struggle with the king (see below). That one matter treated in the compilation was measures taken for defence of the city should be viewed in the context of that struggle. The measures included the attempt to impose a special tax not only on the citizenry but on foreign merchants who did business in London, presumably to finance the costs of other defensive measures, and the command to the aldermen to ensure they were in a position to lead the men of their ward, properly equipped, to fight for the city at short notice. Whether these measures were normal at this period, or an exceptional response to the national crisis, is unclear. However, the aldermen's view of arms was likely the city's way of implementing the requirements of the Assize of Arms.

Mrs. Bateson was surprised to find parishes being used as units of the militia. But if we compare with the militia organization in Norwich, it seems natural enough that the aldermen (whether in person or perhaps by substitute) acted in the role of constable or centenar, commanding units supplied by each parish, conceivably under their own junior officers of the vintenar type. Whether the London companies and units were of approximately 100 and 20 men respectively we cannot say, but it is interesting to note that the 5:1 ratio was fairly close to the proportion of parishes to wards in the city.

The second document is believed to be part of a statement by Robert FitzWalter of what he considered reciprocal rights and duties. The description of military duties, and of the ceremonial surrounding the transfer of military authority from civic officials, at times when the city militia had to be deployed in defence of the city or sent out to fight in the king's army, was followed by a second part, which even more strongly has the tone of a list of claims to territorial authority:

• jurisdiction of his seigneurial court over cases involving the tenants of his soke (unless an offence against London's mayor or sheriff);
• the right to punish felons arrested in the soke, where the stocks or imprisonment were involved (although trial and sentencing remained city prerogatives), as well as the execution of convicted traitors by drowning them in the Thames;
• the advowson of St. Andrew's church;
• the right to be invited to participate in Great Councils of the city; also to attend husting court sessions, be seated there beside the mayor, pronounce the judgements of the court, and assign waifs brought before the court to the custody of whomever he chose (albeit with the mayor's advice).

We have no record of the Corporation's response to FitzWalter's claims, although it is unlikely to have looked favourably on them, as they represented a rival to jurisdictional ambitions of them city government. It appears the city made note of the claims without countenancing them; for four years before his death, Robert tried, unsuccessfully, to take advantage of the eyre of 1321 to have his claims – in very much the same words as in the 1303 document – recognized by the king's justices, although he offered to relinquish some of them. In 1275 Robert FitzWalter II was permitted by the king to give Castle Baynard to the Archbishop of Canterbury for foundation of a friary on the site; but in the grant he reserved to himself and his heirs the appurtenant franchises and rights in London. The legal arguments in 1321 hinged partly on whether such a reservation was legal; the London authorities doubtless maintained that it was not and had done what they could to resist or obstruct the exercise of jurisdiction, which may be the reason for the statement of claims in 1303. In 1347 Robert's grandson tried again, and at this point the Corporation formally repudiated the FitzWalter claims to any legal jurisdiction within London.

This does not mean that such jurisdiction, or the related military service to London, has no basis. On the contrary. While rejecting the family's jurisdictional claim at the 1321 eyre, the same venue was used by city authorities to claim rights to land surrounding St. Paul's, in part on the grounds that the muster and meeting with FitzWalter had traditionally taken place there. Furthermore, the claim is corroborated by an entry in the same early thirteenth century compilation from which the first document above was taken; the entry cites a judicial enquiry, held before the death (1136) of Robert FitzRichard, into fishing rights on the Thames. The king's council, hearing the dispute, concluded that jurisdiction over the stretch of Thames between the castle's site and Staines bridge belonged to the lord of Baynard's Castle, as the king's standard-bearer and protector of the city [Bateson, op.cit., 485]. This jurisdiction must itself have been a thorn in the side of the civic administration.

The FitzWalter claims related to a territory within the city appurtenant to Castle Baynard: a soke that later became a city ward. The castle had been built, probably not long after 1066, as one bookend (the Tower being its counterpart) in the Norman strategy for subjugating London's warlike and independent population. Originally held and perhaps raised by the Baignard family (although there are tantalizing hints of one or more pre-Conquest fortifications in London), they lost it in 1110, after falling afoul of the king. It later came into the hands of the Clare family, strong in eastern England, and (by marriage) to Robert FitzRichard, hereditary steward of Henry I. His son Walter FitzRobert was alleged, at the same period when we hear from FitzStephen of the military strength and prowess of Londoners, to be complicit in a plot against Henry III formed by the lord of Montfichet Castle (situated close to Baynard's), whose power base was also in eastern England, although Montfichet was probably a modest fortification; the information was likely scurrilous and nothing came of it. However, Walter's son Robert FitzWalter (grandfather of the 1303 claimant) was to play a key role in the revolt against King John.

John had already had important dealings with London in the context of the power-struggle during the absentee years of Richard I. Richard's justiciar, William de Longchamp, sought to use the Tower as a fortress against Prince John, and both sides tried to win support from London. In 1191 the city gave its loyalty, and a promise of backing his claim to the succession, to John in return for a grant of new privileges and the right to call itself a commune, which led to the introduction of the office of mayor, a communally chosen focus for local government. After attaining the throne, John was persuaded with a large gift of money to confirm the city's old and new liberties, even though no reference was made in the confirmation grant to either mayor or commune. But John's need for money, leading to heavy taxation of the city as well as demands for further gifts, together with steps he took to undermine certain of London's liberties, soon cost him any popularity he had there.

The Londoners therefore had cause to side with the growing baronial opposition to the king. That one of the leaders of this opposition was the lord of Baynard's Castle may have made an alliance easier to forge. In 1212, while Robert FitzWalter was out of the country, John took to opportunity to have Baynard's Castle demolished. But by 1215 the baronial opposition was so strong that John made an attempt to win back London, by granting a confirmation of all its customary liberties, together with a formal recognition of an elected mayoralty. To no avail. When the forces led by FitzWalter, styling himself Marshal of the Army of God and Holy Church, reached London the citizens either permitted, or at least did not oppose, their entry; there was at least an element within the citizenry that sympathized with the rebels, whose list of demands, presented to the king, included London's grievances.

Magna Carta was the result, but only part of the solution. A baronial committee was appointed to oversee the great charter's implementation, and the mayor of London was made a committee member. The king agreed that FitzWalter's forces should continue to hold the city until the king fulfilled the terms of the charter. FitzWalter distrusted the king and knew that control of the city would be a key factor in final victory. Sure enough, John came to repudiate the charter and gather his forces. The barons invited Prince Louis of France to replace John on the English throne. London contributed to Louis' costs in bringing over a French army; upon his arrival, Louis headed for London. In June 1216 the citizens, with FitzWalter and the mayor at their head, gathered in St. Paul's churchyard and paid homage to Louis as their new king. It was said that FitzWalter subsequently commanded a force of 20,000 Londoners raised to support Louis (although we may be skeptical of the estimate). John's death in October 1216, and Louis' failure to win wider support in England, led to his withdrawal and the accession of John's son as Henry III.

Given these circumstances, and the association of the FitzWalters with London, it is credible that document of 1303 reflects a much older tradition, although adapted to changing circumstances, since some of its elements (such as mentions of mayor and recorder, and the heraldic references describing the banner and referring to the saddle and horse-cover emblazoned with the FitzWalter arms) have a later ring to them. The arrangement described in the document appears to reflect a form of cooperation, to mutual benefit, between the city and the feudal holders of a private jurisdiction (soke) within London. The record of Thames fishing rights attached to the soke suggests the alliance came about even before presumably being put to the test during the reign of John. It was perhaps a marriage of convenience, given the mixed feelings the London authorities would have held towards rival jurisdictions within the city.

Whether the military leadership had at any point become a hereditary right, as the document implies, we cannot be sure, but again it is not implausible that such a relationship might have developed – conceivably at the time of the civil war between Matilda and Stephen – between the city leaders and one of the local castellans who (unlike that of the Tower) had some degree of independence from the king. For how long such an arrangement may have been needed we do not know; even before the mustering ground had been absorbed into St. Paul's precinct and Castle Baynard site given over to the Blackfriars, the city authorities – any sense of indebtedness for Robert FitzWalter's help against King John having faded – may have felt the arrangement no longer useful to the city, perhaps even detrimental on balance, preferring to make other arrangements for the command of the militia, even if some of the ceremonial may have lingered. By 1377, many of the aldermen had sufficient social status to have their own coats of arms, and it was expected that their banners be emblazoned with them.

In the early Anglo-Saxon period, London's still sturdy Roman walls gave it a reputation as a refuge; for example, after Hengist's Saxons had defeated the British forces of Kent, the latter fled to London. The Saxon newcomers did not wish to live within the walls and established a trading settlement, Lundenwic, along the stretch of Thames west of Londinium (the area now remembered as the Strand). This was subject to Viking attacks in 839 and 851, and for a while the city was used as a Danish base. Alfred recaptured it in 883 and three years later Lundenberg had become one of the fortified settlements that were a keystone in his plan to defend Wessex. Lundenwic was abandoned (but left its topographical mark as Aldwych, the 'old wic') as the populace sought safety back in the now-ruinous walled area. Efforts were made to repair and rebuild, including the walls and port facilities, in part to encourage settlers and traders to return. By the 890s London was able to field fighting forces that, in conjunction with other English contingents, captured Danish strongholds in Essex.

As a prospering and strategically located commercial and administrative centre, London continued to be a target. As the next wave of Danish invasions got underway, the city faced, in 994, a major assault by a Viking fleet sailing up the Thames, but the citizens were powerful enough to repulse it. Thanks to its defences (which included London Bridge) and its military organization, the city was able to continue to thwart later challenges, but the defensive capability of the English was being worn down. In 1016 most English leaders conceded the crown to Cnut, but the Londoners preferred to continue resistance, choosing as king Edmund Ironside, who prepared for a Danish assault by repairing city defences and assembling troops there. A series of assaults and sieges by Cnut's forces were repeatedly fought off. But after Edmund's death, the city felt it had little option but to submit to Cnut.

London's importance had not been diminished by its stubborn resistance to Cnut. When in 1066 William of Normandy landed near Hastings, the men of London marched out with King Harold's own forces to meet the Normans in battle. After their defeat, the English forces retreated to London, hoping to hold off William there. William too recognized the strategic importance of the city; after a trial assault by his vanguard was repulsed at London Bridge, he recognized that he stood small chance of capturing the city by force and decided instead to isolate it by subduing the surrounding counties and building a series of strongholds there.

The London contingent at Hastings, which was assigned the prestigious role of guarding the person and standard of the king, had been led by Ansgar the Staller, who had the honorific role of bearing the standard. Ansgar held some kind of position of authority in London over a couple of decades, perhaps through his office of staller. Stallers were royal officials, seemingly with regional jurisdiction, whose title means "stable-master"; they were similar to, and perhaps a forerunner of, the Anglo-Norman constable, an office with a partly military role. They may have been imported from Scandinavia, where stallers had a seat near the king and spoke on the king's behalf in the "thing" court. Ansgar, influential not only because of his hereditary office but also as a landholder in eight counties, was wounded in the battle and carried back to London with the survivors of its continent. Despite his wounds, he was apparently able to take the lead in organizing the defence of the city and in negotiating with William for its submission under favourable terms. Some historians have wondered if , because of the various coincidences in their rights and duties, in Ansgar there was some kind of precedent for the FitzWalter field-marshals of the London militia. It has been suggested [William Page, London: Its Origin and Early Development, London, 1923, 132-36] that one early London soke, whose name might (though probably doesn't) mean "war-man's acre", and which incorporated an area that later became Aldgate ward, was at one time in the hands of Tofig the Proud, another staller and grandfather of Ansgar; but this is a very tenuous stringing together of hypotheses. Page in particular argued for a link between the staller and the constable of Castle Baynard.

It was not uncommon under the different conditions at play in Italy for municipal forces to be captained by members of regional aristocracy, although this could prove politically risky. It would be natural enough for English cities to seek similar wartime leadership from the military class, which had landed and commercial interests within the boroughs in the High Middle Ages, but evidence for such arrangements is as rare as indications of inter-city warfare. At York it was claimed, in a report of an inquest of 1106 into the Minster's customary privileges, that the territory of the canons supplied a leader and standard-bearer for the York militia whenever it went to join up with the king's army, but was not liable to provide such military service if the burgess militia as a whole was not called up; however, we do not know if this leader was one of the knightly tenants of the Minster. It would seem that, as the thirteenth century wore on, the price paid in loss of independence was considered by the London authorities too high to pay for professional leadership of that type. But the city was still capable of raising forces that could on occasion play an important role in national defence and in English civil wars.

FitzStephen's description of London makes reference to the military exercises conducted annually, as well as other sports with a military bent, such as tournament-type activities on the Thames or the frozen marshes, javelin throwing, and hand-to-hand combat. In his opening paragraph, he praises in the same breath the commercial success of the townsmen and their physical prowess, while at the same time boasting of the strength of its fortifications. His estimate of London forces as comprising 60,000 infantry and 20,000 cavalry may be taken as exaggeration; the total population of London around his time is unknown but probably around 40,000 [Derek Keene, in The Cambridge Urban History of Britain, vol. 1 (2000), ed. D.M. Palliser, 196].

Nonetheless, the less specific evidence of other writers of that time supports the notion that London could field a sizable force capable of fighting with prowess. If (pursuing the comparison with Norwich) we can imagine each ward being expected to field at least a centenary, which would represent roughly the properly equipped manpower of the ward, but not necessarily the total available to fight in time of crisis, then London should have been able to raise a few thousand men, some of whom would have been mounted; they might conceivably bolstered by more skilled cavalry, such as the FitzWalter contingent, and knights-in-training residing in or around the city such as FitzStephen describes; Baynard and Montfichet castles may have been some of the baronial households he had in mind as supplying young men carrying out military exercises in the fields around the city. Several prominent London citizens of the twelfth century are known to have had the status of knights [Susan Reynolds, "The Rulers of London in the Twelfth Century", History, vol.57 (1972), 339, 346], although this does not necessarily mean they were military men.

As a geographically and politically strategic location with a defensive wall, London was a target for anyone, Englishman or foreigner, with an eye on the English throne. But the Londoners played more than a defensive role. In the civil war between King Stephen and the Empress Matilda, London threw its weight behind the former, who appeared more disposed tan the latter to entertain city ambitions for greater self-government. In 1141 (with Stephen a captive of the Empress) the Londoners took up arms to expel Matilda from the city and blockaded Geoffrey de Mandeville, her supporter and constable of the Tower, in that fortress. Geoffrey switched sides and led a London force, said to be a thousand strong, to raise the siege of the Bishop of Winchester's castle. And in 1145 we hear of a large army of Londoners that Stephen used to capture Earl Robert of Gloucester's castle at Faringdon.

As internal politics settled down and the attention of the king and nobles turned to foreign wars, there was less need for general musters. The contingents the city raised to join larger armies were typically only a small percentage of what could surely have been raised. In 1336, the king imagined that London could raise and equip a defensive force of 7,200 men, but most such demands were far more down-to-earth. On several occasions the city authorities negotiated with the king on the number of soldiers they would supply, sometimes using the excuse that they did not wish to leave the city itself defenceless, although their concern was probably just as much with limiting the associated costs they would have to pay the troops they raised. Nonetheless, the king looked on populous London as an important source of men, and perhaps even more as a source of manned ships for naval defence. As late as 1453, when parliament granted the king a levy of 20,000 archers to serve (probably in France) for six months at the cost of the localities that raised them, London was assigned the largest single contingent at 1,137 (compared to 152 from York, 121 from Norwich, and 91 from Bristol, and smaller numbers from several other towns; in the event, the total number was reduced to 13,000 and even that was never raised, parliament offering instead to raise money to support the planned military campaign.

During the fourteenth and fifteenth centuries, the London authorities, exercised as much as they were able what they saw as a city privilege of discretion in the number of troops it would supply. Consequently, the monarchy had, in its efforts to put together armies for the war in France, come increasingly to rely on calls for volunteers and on monetary payments in lieu of troops, rather than on civic militia.