Some archaeologists have found four (or possibly five, although one may have been a natural tree throw) large Mesolithic postholes which date to around 8000 BC nearby, beneath the modern tourist car-park. These held pine posts around 0.75 metres (2.5 ft) in diameter which were erected and left to rot in situ. Three of the posts (and possibly four) were in an east-west alignment and may have had ritual significance; no parallels are known from Britain at the time but similar sites have been found in Scandinavia. At this time, Salisbury Plain was still wooded but four thousand years later, during the earlier Neolithic, a causewayed enclosure at Robin Hood’s Ball and long barrow tombs were built in the surrounding landscape. In approximately 3500 BC a large cursus monument was built 700 metres (2,300 ft) north of the site as the first farmers began to clear the forest and exploit the area.