Archaeological excavations in 2009-2011 at Kanaljorden in the town of Motala, Ostergotland in Central Sweden unearthed a great Mesolithic site with ceremonial depositions of human crania in a former lake.
More info :
pasthorizonspr.com/index.php/archives/03/2012/skulls-on-stakes-in-sweden-date-to-the-mesolithic