ARCHAEOLOGISTS are to investigate the keep of a castle which was built on the orders of William the Conqueror to dominate the Viking city of York.

Clifford's Tower, which has served as a prison and a royal mint, as well as the place where Henry VIII had the bodies of his enemies put on public display, will close for a fortnight this month (January).

Experts will take soil samples from several places in the mound of the landmark keep, which is among the most popular attractions in the North with more than 140,000 visitors annually, to better understand its structural stability and shed light on its make-up.

Jeremy Ashbee, head historic properties curator at English Heritage (EH), which runs the site, said the mound could contain material from a Bronze Age burial-mound and a Roman cemetery.

He said: "Its history as a castle starts with William the Conqueror in 1068, trying to subdue the North of England."

The tower, which was originally built by William the Conqueror to subdue the rebels of the north, was twice burned to the ground, before being rebuilt by Henry III in the 13th Century.

It takes its name from when Roger de Clifford was executed in 1322 or treason against Edward II and hanged in chains from the tower walls.

"We think that the mound has become taller and wider during successive re-buildings over nine centuries."

The stone structure of the tower will also be examined as part of essential conservation work.

EH said an initial assessment had found the foundations were in good shape and had confirmed concrete underpinning have taken place twice in the early 20th Century.

The conservation body said the results of the study would be used to determine what can be done to improve the visitor experience at the site.

Liz Page, EH historic properties director in the North, said the work would mean the closure of the tower from January 12 to 23.

She said: "We want to do the tower and its fascinating story justice.

"There are only three information panels to explain the vast history and significance of Clifford's Tower, which is inadequate.

"But before we start looking to the future, we need to look at the past and these works are part of that process."