<P> Evidence of the second phase is no longer visible . The number of postholes dating to the early 3rd millennium BC suggest that some form of timber structure was built within the enclosure during this period . Further standing timbers were placed at the northeast entrance, and a parallel alignment of posts ran inwards from the southern entrance . The postholes are smaller than the Aubrey Holes, being only around 0.4 metres (16 in) in diameter, and are much less regularly spaced . The bank was purposely reduced in height and the ditch continued to silt up . At least twenty - five of the Aubrey Holes are known to have contained later, intrusive, cremation burials dating to the two centuries after the monument's inception . It seems that whatever the holes' initial function, it changed to become a funerary one during Phase 2 . Thirty further cremations were placed in the enclosure's ditch and at other points within the monument, mostly in the eastern half . Stonehenge is therefore interpreted as functioning as an enclosed cremation cemetery at this time, the earliest known cremation cemetery in the British Isles . Fragments of unburnt human bone have also been found in the ditch - fill . Dating evidence is provided by the late Neolithic grooved ware pottery that has been found in connection with the features from this phase . </P> <P> Archaeological excavation has indicated that around 2600 BC, the builders abandoned timber in favour of stone and dug two concentric arrays of holes (the Q and R Holes) in the centre of the site . These stone sockets are only partly known (hence on present evidence are sometimes described as forming' crescents'); however, they could be the remains of a double ring . Again, there is little firm dating evidence for this phase . The holes held up to 80 standing stones (shown blue on the plan), only 43 of which can be traced today . It is generally accepted that the bluestones (some of which are made of dolerite, an igneous rock), were transported by the builders from the Preseli Hills, 150 miles (240 km) away in modern - day Pembrokeshire in Wales . Another theory is that they were brought much nearer to the site as glacial erratics by the Irish Sea Glacier although there is no evidence of glacial deposition within southern central England . </P> <P> The long distance human transport theory was bolstered in 2011 by the discovery of a megalithic bluestone quarry at Craig Rhos - y - felin, near Crymych in Pembrokeshire, which is the most likely place for some of the stones to have been obtained . Other standing stones may well have been small sarsens (sandstone), used later as lintels . The stones, which weighed about two tons, could have been moved by lifting and carrying them on rows of poles and rectangular frameworks of poles, as recorded in China, Japan and India . It is not known whether the stones were taken directly from their quarries to Salisbury Plain or were the result of the removal of a venerated stone circle from Preseli to Salisbury Plain to "merge two sacred centres into one, to unify two politically separate regions, or to legitimise the ancestral identity of migrants moving from one region to another". Each monolith measures around 2 metres (6.6 ft) in height, between 1 and 1.5 m (3.3 and 4.9 ft) wide and around 0.8 metres (2.6 ft) thick . What was to become known as the Altar Stone is almost certainly derived from the Senni Beds, perhaps from 50 miles (80 kilometres) east of Mynydd Preseli in the Brecon Beacons . </P> <P> The north - eastern entrance was widened at this time, with the result that it precisely matched the direction of the midsummer sunrise and midwinter sunset of the period . This phase of the monument was abandoned unfinished, however; the small standing stones were apparently removed and the Q and R holes purposefully backfilled . Even so, the monument appears to have eclipsed the site at Avebury in importance towards the end of this phase . </P>

Where did the stones of stonehenge come from