The four criteria for assessing class importance apply to quadrangular castles as follows:

Period (currency): Restricted. The tradition of building quadrangular castles lasted for about 200 years, starting in the late 13th century, with most in the 14th, and the last in the late 15th century.

Rarity: Rare. A total of sites 64 is known, of these 20 are of northern style and 44 southern style. The number known is unlikely to increase as most have probably been identified in some way.

Diversity (form): Very high. The classification shown above illustrates the wide diversity of this class of monument. In addition to the division into northern and southern types, there is also the question of towers, gate houses, barbicans, concentric or non-concentric enceintes, and a variety of external defences.

Period (representativity): Very high. Although there are many classes of medieval monument that of quadrangular castles is one of the few devoted to defence and important residence, and displaying fine building styles.

Assigning scores to these criteria following the system set out in the Monument Evaluation Manual, quadrangular castles yield a Class Importance Value of 45. This is two thirds up the range of possible values (max=64), reflecting the wide diversity and rarity of this class of monument.