It is also worth remembering that henges are not defensive structures. The comparison between henges and defensive structures such as hillforts is easy to make. A typical Hillfort will have its ditches outside the earthen banks and will generally have been built over a much larger area on high defendable ground. Some appear to be semi-defensive structures, normally found on high ground. Although they may well have performed the same function as hillforts they share similarities with henges.
Discontinuous ditches lie inside the earthen banks.
They appear to be unique to the British Isles. Please feel free to contact me if you have information about any confirmed henges elsewhere in the world. Finally I'd just like to say a word on Crop Marks. Click here to see a Crop Circle . Crop Marks, on the other hand, are a recognised archaeoligal feature.