There are roughly 175 miles between Pembrokeshire in Wales and the Salisbury Plain in England. The first represents the location of neolithic quarries from which stone was extracted some 5,000 years ago. The second is the famous Stonehenge ― a prehistoric shrine whose origins remain a subject of heated debate between scholars.
The relation between the two places ― besides the distance ― has long been a subject of extensive research. While the ancient world was no stranger to monolithic structures which would be difficult to construct even by today’s standards, the difference between Stonehenge and other structures lies in a choice to neglect local stones and, shall we say, rather “import” them from a great distance.

Long shadows from the early morning sun at Stonehenge
With a number of questions still open, scientists on the Stonehenge case announced in February 2019, that they just might be one step closer to solving the mystery.
A discovery by an archaeology team led by Professor Mike Parker Pearson of University College London’s Institute of Archaeology of massive stone-cutting tools found in Pembrokeshire has shed new light on this complex debate.
Archaeologists claim to have found the prehistoric tools used to quarry the original standing stones that date from the earliest phases of Stonehenge, just after the religious site adopted its monumental stone features.

View of the western half of the Preseli Hills taken from 1/2 mile north of Crymych on A478. Photo by Tony Holkham CC BY 3.0
The tools were found on the northern slopes of the Preseli Hills in Pembrokeshire, southwestern Wales, where two former quarries were located.
Experts who had used chemical analysis to track the bluestone from Stonehenge to Pembrokeshire claim that there are at least three more locations that were used to quarry stones for the sacred site in Salisbury Plain.

View from Carn Menyn eastwards towards Foel Drygarn (centre-left) and Y Frenni (centre-right) in the distance. Photo by Tony Holkham CC BY SA 3.0
The discovery includes several hammerstones used for inserting and forcing in the wedges, which would, in return, cause for the large parts of the stone to detach from the rock. The wedges were made from sandstone, and 15 of them have been discovered during this particular excavation.
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Apart from the tools, traces of V-shaped slots were also discovered in two columns of what was once the Pembrokeshire quarry. The slots seem to have been fitted, but for some unknown reason, never used. It was as if the ancient stonemasons had left it there as evidence of their methods and work.

Stonehenge
Regarding the discovery, as well as the implications it presents, Pearson gave a statement for the British archaeological journal Antiquity soon after they went public with the excavation results:
Every other Neolithic monument in Europe was built of megaliths brought from no more than 10 miles away. We’re now looking to find out just what was so special about the Preseli Hills 5,000 years ago, and whether there were any important stone circles here, built before the bluestones were moved to Stonehenge.

A standing stone in the Preseli Hills mountain range, Pembrokeshire, Wales. This stone is one of the bluestones from this area which were used to construct the inner circle of Stonehenge.
Theories are currently being spawned on how and why were these prehistoric men so keen on crossing such a distance while transporting stones that weighed up to 4 tons each.
As for transport, there are two dominant options. First of them ― and perhaps the most logical ― was that the stones were carried on rafts, or catamaran-like boats along the coast, and then transported via the Avon river to within 20 miles of Stonehenge’s location.

The prehistoric monument of Stonehenge in England. Focus is on the grass.
The second theory is presumed to be dominantly by land. The idea of transporting 79 huge pieces of stone across the country by land must have been a very strong demonstration of might ― one that could have symbolically consolidated a power struggle between rival tribes and clans that inhabited Britain in the third millennium B.C.
In such case, they would probably be carried by stretchers, sleds or rollers facing an unforgiving terrain, besides the long distance. The use of rivers would be fairly limited in this case, therefore demanding tons of manpower to be employed constantly.
These two options offer a solution on how the bluestones of Stonehenge were transported. However, “why” is an entirely different issue.

Rare and beautifully executed Engraved illustration of Druids Worshiping at Stonehenge, England in Ancient Times Engraving from The Popular Pictorial Bible,
By analyzing the bones excavated in the vicinity of the site, the scientists have determined that a number of them originated from the very area where the stones can be traced. Therefore, it is possible that the community that built Stonehenge had migrated from southwestern Wales, and possibly even brought the stones that hold such great cultural influence with them.

Photography of Stonehenge at the sunset
Some scientists argue that perhaps the first stones that form the foundation of the Salisbury Plain might have served earlier as part of a similar structure, somewhere around Pembrokeshire.
This would mean that there was an original, proto-Stonehenge in Wales, before the one in England. If true, this theory could easily shake many notions regarding the origins, the culture and the ritual role of Stonehenge. However, evidence for such groundbreaking claims is yet to be found.