Just as a successful attack on a major fortification required a combination of different resources on a large scale, so also the defence needed to adopt a range of measures where possible. Whether there was a defence against mines depended in part on the site, and on how deep the ditch was. The defence against artillery relied both on the strength of the wall and towers, but also and increasingly on the design of outer layers of defence, ditches and wet moats, and second walls. In the ideal design, the combination of ditch and outer wall would protect the inner wall from bombardment, but to defend the outer defences against assault meant, if possible, providing a concentric design that enabled the defence to shoot from two levels simultaneously, which in turn limited the distance between the two walls. Gates were always important, and it is not to underestimate their role as a visual statement of the importance of the owner (or of the self-esteem of the city) to note that since time immemorial they had also been the subject of particular care when it came to defensive considerations. With the doubling up the curtain walls and the ditches, gateways also needed an outer layer if they were to fit the new configuration, requiring some kind of barbican.

Extreme measures might be taken, as with the building by the Moroccans of a complete new town with modern defences after the close-run siege of Algeciras in 1278–9, and if this massive undertaking was not only for these reasons, its timing, was nonetheless suggestive. Converting old defences or building new ones, even if using sites where some of the weaknesses could be compensated for by the topography was expensive. Fortresses built or rebuilt during the thirteenth century, such as the new castles and city walls in Capetian France, several of those put up or restored in the Latin east, or the work of Frederick II in Italy, or Edward I's in Wales, were of unprecedented physical strength. They were also prodigiously costly, so much so that the later generation of Edwardian castles was never completed.