Tunnels built into the side of an ancient mound in Wiltshire in the late 1960s are to be filled in because of fears the monument could collapse.
English Heritage has been working at the site for months
The tunnels in Silbury Hill near Avebury have been shored up and will soon be filled with chalk.
The tunnels were created during an archaeological dig in 1968.
Last year the tunnels were opened by English Heritage which found they were at risk of collapse, which could have affected the whole monument.
Fragments of antler
Once the monument was made safe archaeologists used the opportunity to find out how Neolithic man built the mound.
Fragments of an antler - believed to have been used as a pick to quarry the chalk during the construction - were found.
Silbury Hill is believed to be the tallest prehistoric man-made mound in Europe and one of the world's largest.
Archaeologists calculate it was built more than 4,000 years ago.
The hill was built in layers using turf, earth, gravel and sand for the lower levels and chalk for the upper.