A detailed laser-scan survey of the entire monument has discovered 72 previously unknown Early Bronze Age carvings chipped into five of the giant stones - graffiti added when the enormous slabs were already 1000 years old. All of the newly discovered prehistoric art works are invisible to the naked eye. In the Early Bronze Age the images would have been clearly visible. Of the 72 newly discovered images, 71 portray Bronze Age axe-heads and one portrays a Bronze Age dagger.
     Prior to the laser survey, 46 other carvings (also of axe-heads and daggers) were known or suspected at Stonehenge. The laser-scan survey has confirmed the existence of those other images and provided more details about them. The new discoveries almost treble the number of carvings known at Stonehenge - now the largest single collection of prehistoric rock carvings in southern Britain.
     The main phase of the monument - built in the middle of the 3rd millennium BCE - was designed primarily as a solar temple, aligned on the mid-winter and mid-summer solstices. The carved axe-heads and daggers belong to the enigmatic period of 1800-1500 BCE, when vast numbers of individual monumental tombs were constructed around Stonehenge. In Indo-European tradition axe-heads were often associated with storm deities, and some surviving European folklore beliefs suggest that upwards-facing axe blades were used to protect crops, people and property against lightning and storm damage. Every one of the Stonehenge axe-head images have their blades pointing skywards, while the daggers point downwards.
     The survey and analysis has yielded other new insights. The entire temple was constructed to be viewed primarily from the north-east - the side approached by what archaeologists have long believed to be a processional way, aligned with the solstices. One of the stones at the now ruinous south-west side of the monument was also very deliberately worked and shaped to allow a line of sight through to the setting sun on mid-winter's day. The implication is that at some stage in its history there was a deliberate attempt at its destruction.
     Particularly puzzling is the discovery that the masons used two different techniques. Work on the monument's great circle (both uprights and lintels) was accomplished by working parallel to the long sides of the stones, while the 5 stone trilithons within the great circle (the horse-shoe arrangement of linteled stones) were dressed at right-angles to the sides of the stones. This previously unknown fact suggests that the great trilithons may have been constructed slightly before the great circle rather than being contemporary with it.

Edited from English Heritage, The Independent, The Guardian (9 October 2012)