Since the year 1990 in Germany´s South sensational discoveries of prehistoric cairns in so called quarries are made. They are larger und higher than every noted monument of the Megalithic Period in North Germany and whole Europe. 25 passage graves are known and explorable anytime. The construction of monuments within the rock of a slope is archeologically related to Etruscan rock-necropolises like Banditacci in Cerveteri or Crucifisso del Tuffo in Orvieto.
Please do the math and watch the videos. And if you like recommend them.
Megalithic Mysteries of Germany, Part 1 – 3