Stumbled on this small charming enclosure while ambling around the New Forest. It's not very big, popular with local bovine herds, probably no more than about 20-25m in diameter and the banks no more than 1.5m high (mostly on the southern side). I imagine in the winter months it's probably very boggy around here and the northern and eastern sides are bounded by the beginnings of the Beaulieu River which acts as a natural defence. Pastscape describes the earthwork as a Bronze Age enclosure or early Iron Age univalate Fort. I'd go for the former as the earthworks don't seem like they were ever defensive and more about preserving a bit of dry ground in a very flat area. There are also a number of (presumably) Bronze Age barrows nearby which might support that.
Another interesting feature about a mile to the west is Row Hill which has 3, or possibly 4, long mounds on top of it. These are quite substantial, the biggest being about 2m high and about 15m long all running parallel. I've no idea how old they might be and would hesitate to call them long barrows. WW1 activity in the forest might be one explanation for their presence as there are currently notice boards all over the place warning you against straying from the path due to unrecovered ordnance. After a hundred years - I ask you?!