A circular rampart is an embankment built in the shape of a circle that was used as part of the defences for a military fortification, hill fort or refuge, or was built for religious purposes or as a place of gathering.
The period during which these structures were built ranged from the Neolithic to the Middle Ages.
Wikipedia https://en.wikipedia.org/wiki/Circular_rampart
landingPages.LANDING_PAGE.DETAIL.ADDRESS Oost-Souburg 4388, Netherlands
landingPages.LANDING_PAGE.DETAIL.COORDINATES 51°27'47.674" N 3°36'15.455" E