Heavy rainfall has seen a moat form around a 4,000-year-old prehistoric hill.

Silbury Hill is the largest artificial mound in Europe - a 40m chalk site at the Avebury World Heritage Site.

Downpours have seen a large horse-shoe shaped lake formed around the hill - making it look like an ancient fort or motte and bailey castle.

Archeologists know little about the purpose of the mound but it is believed that it took around 18 million man hours to build it - likely by hand.

The design has previously been compared to the ancient Egyptian pyramids, which were built around a century earlier.

Tim Daw, local expert on ancient monuments, told the BBC it is possible when the mound was built it featured the moat as a permanent feature - as the water table was much higher then than it is today.

English Heritage's senior properties curator Win Scott says that the moat is known to form seasonally and will naturally drain away over time.

Flooding at the site has occurred most recently in 2000, 2007 and 2013, and does not prevent visitors from viewing or accessing the site.