The builders placed the bones of deer and oxen in the bottom of the ditch, as well as some worked flint tools.
The bones were considerably older than the antler picks used to dig the ditch, and the people who buried them had looked after them for some time prior to burial.
If this were the case, it would advance the earliest known stone structure at the monument by some 500 years.
Three of the posts (and possibly four) were in an east-west alignment which may have had ritual significance.
Another Mesolithic astronomical site in Britain is the Warren Field site in Aberdeenshire, which is considered the world's oldest Lunar calendar, corrected yearly by observing the midwinter solstice.
Stonehenge is a prehistoric monument in Wiltshire, England, 2 miles (3 km) west of Amesbury.
It consists of a ring of standing stones, with each standing stone around 13 feet (4.0 m) high, 7 feet (2.1 m) wide and weighing around 25 tons.
This first stage is dated to around 3100 BC, after which the ditch began to silt up naturally.