This cruciform earthwork has been classified as a Pillow Mound, which is a type of structure intended for use as rabbit warrens.
They were introduced by the Normans but continued to be built until much later.
Not easy to see in these pictures, because of the overgrowth of heather and the wrong lens on the camera, is an equi-armed cross of c.30m span. The axes are NE/SW and NW/SE, the flat-topped bank is c.2.5m wide and 0.6m or so high.
There were no signs of any animal burrows or entry holes of any kind. There was ponding of surface water against the uphill side of the NE/SW arms that would seem to indicate its unsuitability as a home for burrowing animals.
References
- National Monuments Record of Wales: Coflein database - site details.