Because the Kerdruelland menhirs have been preserved in mud and silt for 4,500 years, they should offer important new information on how such alignments were created and why. At the well-known sites, such as Carnac and Stonehenge, some of the stones have been moved or propped up or stolen or added over the centuries. Here the stones, up to 2m long, lie just as they did after they were felled four-and-half millennia ago.
At neolithic sites elsewhere, the soil of the period has been eroded by the ravages of time and man. At Kerdruelland, the neolithic sub-soil - the soil on which the stones were erected - has been preserved intact. This offers a cornucopia of possible new archaeological finds. Already, a brief dig has yielded a rich harvest of flint tools and shards of pottery.
Just as importantly, the preservation of the neolithic sub-soil will help the experts to discover traces of the original earthworks and study the methods of assembling and positioning the menhirs.
THe quoted portion explains why this site is important. Apparently, it was built and toppled in a relatively short span of time so we're not dealing with multiple episodes of rebuilding. Pretty cool. Read the whole thing.