Construction of massive pyramids in Bosnia at that period is not believable. Curtis Runnels, a specialist in the prehistory of Greece and the Balkans at Boston University, notes that "Between 27,000 and 12,000 years ago, the Balkans were locked in the last Glacial maximum, a period of very cold and dry climate with glaciers in some of the mountain ranges. The only occupants were Upper Paleolithic hunters and gatherers who left behind open-air camp sites and traces of occupation in caves. These remains consist of simple stone tools, hearths, and remains of animals and plants that were consumed for food. These people did not have the tools or skills to engage in the construction of monumental architecture."