A cutting-edge laser scan of Stonehenge has shown how Britain's enigmatic neolithic monument was built to enhance the dramatic passage of sunlight through the circle of stones at midsummer and midwinter.

The slabs were intended to appear at their best in the dawn light on the longest day of the year and at sunset on the shortest, the scan for English Heritage found.

The two solstices attract thousands of visitors to Stonehenge, which dates back some 5000 years.

The 3D scan showed the stones to the northeast were carefully "pick-dressed" - worked to be smoother and neater than the other columns - creating a more dramatic spectacle from that angle.

Those stones were set where they would be seen first by people approaching the monument from the northeast along the Avenue, a processional route that would have been particularly spectacular at the midwinter sunset.

The scan uncovered 71 new images of axe-heads carved into the surface, doubling the number of known such carvings recorded in Britain.

It also showed up damage and graffiti from Georgian and Victorian visitors.

In the 19th century, visitors could hire chisels at the site to hack off their own souvenirs from the stone.

According to the new evidence, the axe-head carvings were made in the Early Bronze Age, around 1000 years after the first builders got to work at Stonehenge.

The lofty stones were transported some 400km to the site in around 2100 BC.

Archeologists are still puzzled as to how the stones, weighing up to 45 tonnes, were made to stand upright.

- Reuters