From memory , working for once I hope , 20m , but no central mound or depression , the bank is 1m high. I'm thinking along the lines of it being an enclosure for animals without an entrance ? they could always jump , and if it turns out otherwise it's a bonus.

juamei, hello, when I dowse a polygon( circle) it has two important strong flows of energy around a centre spot.
The outer flow of energy is at 56 feet 7 inchs circumference, from a centre spot, a diameter of 113 feet 2 inches ( showing My age now ) aprox 34 metres.
These measurements never vary.
If You or anyone else get the opportunity to check for this measurement, I would appreciate.
It may be the outer circumference.
K.