Modern technology has revealed some ancient secrets that Stonehenge has kept hidden for thousands of years:
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.
All of the newly discovered prehistoric art works are invisible to the naked eye – and have only come to light following a laser-scan survey which recorded literally billions of points micro-topographically on the surfaces of the monument’s 83 surviving stones. In total, some 850 gigabytes of information was collected.
Detailed analysis of that data – carried out on behalf of English Heritage - found that images had been engraved on the stones, normally by removing the top 1-3 millimetres of weathered (darker coloured) rock, to produce different sized shapes. Of the 72 newly discovered images revealed through the data analysis, 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 – mostly identified visually back in the 1950s. The laser-scan survey has now confirmed the existence of those other images and provided more details about them.
The 72 new ‘rock art’ discoveries almost treble the number of carvings known at Stonehenge – and the monument’s largely invisible art gallery now constitutes the largest single collection of prehistoric rock carvings in southern Britain.
It's important to note that Stonehenge was almost a 1000 years old when the first carvings were made, so we should be careful to segregate cultural meaning to the various periods of the monument's existence. The full report ("Stonehenge Laser Scan: Archaeological Analysis Report", PDF download) contains an image of the axe-head carvings:
I definitely recommend reading the entire report, as it contains a number of interesting discussions about Stonehenge that you probably won't find in the media reports on this project.
Update: Some commenters (below) have suggested the carvings look as much like mushrooms as they do axeheads, which might bring you meaning to the name Stonehenge. What say you?