The four criteria for assessing class importance apply to Roman fishponds as follows:
- Period (currency): Restricted. The tradition of constructing and using Roman fishponds spanned the 1st to the 4th century.
- Rarity: Very rare. Less than 50 Roman fishponds have been recorded to date.
- Diversity (form): Low. The form, size and complexity of Roman fishponds discovered to date indicates low variability. No firm differences in type can be detected on the basis of ground plan and the arrangement of components.
- Period (representativity): Low. Roman fishponds are just one of many classes of Roman monuments and provide limited information beyond their use and construction.
Assigning scores to these criteria following the system set out in the Monument Evaluation Manual, Roman fishponds yield a Class Importance Value of 22. This lies well under the mid point of the range of possible values (max.=64), reflecting their low representativity and relative homogenity of purpose and design. Examples representing the full range of types, and variations in size and situation, must also be included in the sample of nationally important Roman fishponds. It should be noted that most are located through excavation and so are destroyed; few are available for preservation.