Chester (placename element)
The English place-name Chester, and the suffixes -chester, -caster and -cester (old -ceaster), are commonly indications that the place is the site of a Roman castrum, meaning a military camp or fort (cf. Welsh caer), but it can also apply to the site of a pre-historic fort.
Source: Wikipedia — Chester (placename element) (CC BY-SA 4.0)