Seahenge as it was discovered at Holme-next-the-Sea
A Norfolk museum closing to the public for four months from Saturday while the central stump of a Bronze Age oak circle known as Seahenge is installed.
The Lynn Museum in King's Lynn has seen a large increase in visitors since opening a gallery in 2008 devoted to the 55 outer timbers of the circle.
Work is now taking place to create a mount for the 4,000-year-old stump which weighs more than one tonne.
Seahenge was discovered emerging from a beach at Holme-next-the-Sea in 1998.
Its 55 oak posts in a circle with a central stump sat unnoticed and undisturbed off the Norfolk coast for almost 4,000 years, but became exposed at low tides after the peat dune covering it was swept away by storms.
Archaeologists believe between 50 and 80 people may have helped build the circle, possibly to mark the death of an important individual.
The Seahenge gallery at the museum is drawing thousands of visitors
The timbers were excavated in 1999 and went to the Bronze Age Centre at Flag Fen near Peterborough to be studied and the preservation programme began. To finish the conservation programme they then went to the Mary Rose Trust in Portsmouth.
But at 8ft (2.5m) in height the preservation process for the central stump has taken longer.
Derrick Murphy, from Norfolk County Council, said: "Why our ancestors built Seahenge remains a mystery, yet we can state categorically that it is one of the most significant historical discoveries ever to be found in Britain.
"The installation of the central stump within the gallery at the Lynn Museum marks a fitting end to this chapter of the story of Seahenge."