The Stone-piles were, in fact, the key to the fecundity of the Trolls of the Trollshaws. They could only be destroyed during times when Sauron was inactive . If someone had deduced the connection in the first millenium of the Third Age, much local history would have been different. As it was, the piles emitted periodic bursts of energy that tripled or bettered the fertility rate of any Trolls in their immediate area. The less they were worshipped, the more frequent the energy outbursted. The Trolls of Rhudaur, therefore, were always subject to sudden unexplained surges in number, and exterminating them was next to impossible.