The great walled cities of the Levant — Antioch, Tripoli, Beirut, Tyre, Acre, Caesarea, Jaffa, Ascalon and Jerusalem itself — were the anchors of the Frankish defence network. Cities that could withstand extended sieges, particularly coastal cities that could be resupplied by sea, were invulnerable to any but the most tenacious opponents. Throughout most of Outremer’s history, the armies opposing the Franks were too transient to sustain lengthy sieges and frequently disintegrated or withdrew at the mere approach of the Frankish field army.
The eminent cities and smaller walled towns in the interior such as Hebron, Bethlehem, Tiberias and Nazareth were supported and reinforced by castles great and small. The most famous castles are the large concentric ones that represented the pinnacle of military architectural development of the period, such as the now-famous Crac de Chevaliers, Montfort (Starkenburg) and Kerak. However, most crusader castles were much simpler and smaller, often little more than a tower or a perimeter wall. Altogether roughly 100 Frankish castles have been identified.
For centuries, it was presumed the Franks mostly adapted existing defensive structures in already-established population centres. Archaeological surveys of the last quarter-century, however, prove that nearly half the castles built in the twelfth century were constructed in rural and remote areas of the country near Oriental Christian monasteries or settlements. There is ‘almost no correlation between the location of the castles and areas of military confrontation’.[i] In short, the purpose of many castles was not so much defence as administration; they were first and foremost symbols of power and presence and only secondarily places of refuge in an emergency.
Because of the speed with which the Frankish army could mobilise, castles of the pre-Saladin era needed to be capable of holding out no more than one week. Only in the later twelfth century did the Franks start constructing the massive castles we associate with the term ‘crusader castles’. In part, this was a response to the threat posed by Saladin and, in part, necessary to compensate for improvements in Saracen siege equipment and tactics. This dictated the construction of thicker and higher walls as well as multiple lines of defence, resulting in concentric castles, such as Crac de Chevaliers.
Immense fortifications, however, required ample garrisons of trained fighting men. Records tend to mention only the number of knights assigned to a garrison because contemporaries knew that for every knight, there were also sergeants, archers, squires and servants of roughly ten men per knight. Thus, castles garrisoned by, say, forty knights were not defended by forty men but by four hundred men, 10 per cent of which were knights.
Furthermore, these new castles were extremely expensive to build and maintain. Based on thirteenth-century Templar records for the reconstruction of the castle at Safed, castle construction cost approximately one million Saracen bezants; in modern terms, roughly one billion pounds. The modern equivalent of the annual maintenance costs comes to roughly forty million pounds. In the twilight of the crusader states, it was as much the inability to finance such expenses as the decline in manpower reserves that doomed the Frankish kingdom. Furthermore, the great concentric castles of the thirteenth century may have had the negative side effect of encouraging more passive tactics, even though offensive operations had served the kingdom so well in the past.
[i] Ronnie Ellenblum, Crusader Castles and Modern Histories (Cambridge: Cambridge University Press, 2007), 172.
The bulk of this entry is an excerpt from Dr. Schrader's comprehensive study of the crusader states.