Siege Practicality of the Rectangular Keep

Castle construction was closely related to the development of siege warfare (Jones 163). This is because the development of these private fortifications made warfare trickier (Jones 163), and the very art of “siegecraft was developed to overcome defensive obstacles” (Jones 165). Though they were largely responding to changes in siege engines, the castle’s “defenses appear to have kept pace with changes in weaponry” for the most part (Jones 165). They maintained their importance, and seizing these defenses was often a crucial part of warfare (Gillingham 79). In his book The Medieval Siege, Jim Bradbury conjures a similar scene by writing:

The rapid spread of castles as the main form of fortification inevitably affected warfare. From the eleventh century, siege warfare was dominated by castles, and this central medieval period was an age of war: the Norman Conquest of England, the civil war of Stephen’s reign,… It was an age of war, yet marked by only a handful of pitched battles. (Bradbury 71)

Jim Bradbury further claims “that warfare consisted of perhaps one per cent battles and ninety-nine per cent sieges” (71); however, Bernard Bachrach asserts that “the major wars of the period 950-1200, which Bradbury sees largely in terms of castle warfare, were in fact, focused upon the old Roman cities and lesser fortifications” (128). Bachrach believes that this focus given to castle sieges by historian is driven by an emphasis on knightly warfare (127). However, with this in mind, it seems certain that the threat of a siege still existed in England, even if it was limited to knightly warfare.

This threat is demonstrated by an event that happened in the reign of Henry I. Ordericus Vitalis writes in the Ecclesiastical History of England and Normandy that upon being summoned by King Henry to “plead in his court to an indictment containing forty-five counts of offense,” Earl Robert de Belesme choose to flee instead (331). In response:

…he [King Henry] proclaimed him [Robert de Belesme] a traitor unless he returned, and submitting to judgment, was ready to do right. The rebel, being once more summoned to appear in court, gave a flat refusal, and, what is more, lost no time in adding to the fortifications of his castles in every quarter by trenches and walls, and in demanding aid from his Norman kinsmen, and the alien Welsh, and all his allies. The king called out the whole military array of England, and laying siege to Arundel castle, which stands near the sea-coast, he erected forts, and stationed his officers in them with bodies of troops for three months (Ordericus Vitalis 332)

Admittedly, as it is described by Ordericus Vitalis, this particular siege ended on a rather flat note with Arundel castle calling a truce in order to ask the accused earl for permission to surrender, which he reluctantly gave (332). However, sieges did not necessarily end this amicably. The primary purpose of the tower was to protect inhabitants that had no intention of surrendering, and this purpose is evident in the castle’s very architecture.

Based upon their construction, stone rectangular keeps had some advantages in the siegecraft. “Masonry offered far greater resistance against stone-throwing siege engines” than the wood of previous castles, and it was certainly harder to set on fire or physically assault (Jones 172-173). The height of these massive and thick walls “increased the dominance of the defenders and worsened the inferior position of the attackers” (Lepage 54). The tall walls of the design thwarted potential escaladers (Jones 173). It likely would require a longer ladder, and the longer climbing time was ample time for the defenders to aim at the scaling invaders. The walls had to be thick in order to resist the battering ram (Lepage 46), and they were further “strengthened by buttresses” (Toy 66). There was a similar tactic implemented in landscaping the surrounding areas with moats that hindered the approach of siege towers (Jones 173). Other smaller details were surprisingly adapted for defense too. The spiral staircases, for example, “turn[ed] counterclockwise so that an aggressor was forced to present his vulnerable right side [since] the shield was always worn on the left arm” (Lepage 52).

The roof of the keep defending the keep often had a crenellated parapet, which was a defensive advantage (DeVries & Smith 230). This crenellation was comprised of the merlon and the crenel (Lepage 48). The crenels were the gaps from which the castle inhabitants could attack the invaders (either by shooting arrows or throwing something); whereas, the merlon were the vertical structures that the shooters could use as cover while reloading their weapon or grabbing something else to chuck at the invaders (Lepage 48).


chaoticblackcat. “Dover Keep’s Crenellation.” 14 July 2014.

“By the mid-twelfth century, even minor castles were able to resist aggressive action for considerable periods” (Jones 173). With adequate provisions, these stone fortifications could withstand the sieges of their day (Jones 173).  In fact, during their prime, these towers mainly fell due to “treason, attrition, or surprise” (Lepage 54). As a result, the time it took to siege the castle could drag on for quite a while with an average “between four and six weeks” (Jones 173).

However, as time wore on the rectangular keeps proved that they did have some disadvantages alongside their advantages (Gies 24). One of the castle’s defensive actions consisted of “plunging fire or vertical flanking,” which involved shooting arrows downward (Lepage 49). Unfortunately, the logistics of the height combined with this defensive tactic resulted in blind spots at the tower’s base that “afforded shelter to attackers in the form of ‘dead ground’ that defensive fire could not reach” (Gies 24). The response designed to overcome this problem was hoarding (Lepage 49). “A hoarding, also called hourd, brattice or propugnacula, formed a wooden balcony made of removable scaffolding” that was attached to the wall and constructed over the blind spot (Lepage 49). An example can be seen below. In this French reconstruction, the hoarding is the dark grey wooden structure that tops the castle’s walls.


App1990. “Carcassonne Wall South.” Wikimedia Commons, 29 Aug. 2013, Accessed 04 Dec. 2016.

Sometimes they were constant structures left there all year round; other times they were temporary and only brought out when needed (Lepage 49). However, the hoarding was, in many ways, an inadequate solution (Lepage 52). As wooden structures, they were susceptible to fire; they obscured crenellation, and they required loopholes to overcome their own blind-spots (Lepage 52). At the end of the 13th century, they had evolved into “permanent masonry machicolation” (Lepage 52).

The donjon’s entrance proved to be one of its weakest spots as well (Lepage 52). Attempts were made to counteract this. Aware that it was a potential vulnerability, keeps usually had “only one entrance” (Lepage 52). It could be “access[ed] only by a removable ladder or a spiral staircase” built in a masonic structure called a forebuilding” (Lepage 52). The door itself was built specifically narrowed so that whole armies would have to go through the space one by one (Lepage 52-53). Due to the nature of its construction, it could be “closed and blocked from inside by means of strong transverse beams” (Lepage 53).

When analyzing the siege practicality of this castle design, it is important to remember the perspective of the time period. In the beginning, the keep’s advantages seem to have outweighed the disadvantages. After all, keeps were constructed in England for roughly a hundred years during the twelfth century (Gies 24). However, as siegecraft evolved, problems developed. For example, the rectangular corners proved to be “vulnerable to the sapper, or miner, and the battering ram” (Gies 24-25). The rectangular keep might seem rather primitive in light of later developments, but “without the great stone-throwing machines known as trebuchets, there was not much an enemy at the gates could do, beyond mounting
a blockade and trying to starve a garrison into submission” (Cawthorne, para. 30).

 Works Cited

App1990. “Carcassonne Wall South.” Wikimedia Commons, 29 Aug. 2013, Accessed 04 Dec. 2016.

Bachrach, Bernard S. “Medieval Siege Warfare: A Reconnaissance.” The Journal of Military History, vol. 58, no. 01, 1994, pp. 119-133. JSTOR, Accessed 10 Nov. 2016.

Bradbury, Jim. “Chapter 4: Kings, Counts, and Castellans, 1050-1200.” The Medieval Siege. The Boydell Press, 1992.

Cawthorne, Ellie. “Castles of the Conqueror.” BBC History Magazine, 11 Oct. 2016. Accessed 29 Nov. 2016.

chaoticblackcat. “Dover Keep’s Crenellation.” 14 July 2014.

DeVries, Kelly, and Robert Douglas Smith. “Chapter Nine: Stone Castles.” Medieval Military Technology, 2nd ed., University of Toronto Press, 2002. pp. 223-260.

Jones, R.L.C. “Fortifications and Sieges in Western Europe c. 800-1450.” Medieval Warfare: A History, edited by Maurice Keen, Oxford University Press, 1999. pp. 163-185.

Gies, Joseph, and Frances Gies. “Chapter 1: The Castle Comes to England.” Life in a Medieval Castle. Perennial Library, 1974. pp. 8-31.

Gillingham, John. “An Age of Expansion c. 1020-1204.” Medieval Warfare: A History, edited by Maurice Keen, Oxford University Press, 1999, pp. 59-88.

Lepage, Jean-Denis, G. G. “Chapter 2: The Revival of Military Architecture from the 10th to the 12th Centuries.” Castles and Fortified Cities of Medieval Europe: An Illustrated History. McFarland & Company, Inc., Publishers, 2002. pp. 28-106.

Toy, Sidney. “Chapter VII: Rectangular Keeps or Donjons.” Castles: Their Construction and History. 1939. Dover Publications, Inc., 1985. pp. 66-81.

Vitalis, Ordericus. The Ecclesiastical History of England and Normandy. Translated by Thomas Forester, London: Bohn, 1853. E.J. Pratt Library, University of Toronto, Archive, Accessed 26 Nov. 2016.



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