Viking glass bead, and precious metal, kiln. In order to keep the maximum heat in the center, the stone surrounding has to be repeatedly watered, which also prevents the wooden frame from smoldering. Such kilns could reach temperatures of up to 1600 degre
Maybe over time, and after many rains, a stream was rerouted through the old temple ruins. It would probably be where the Impions would get their drinking water from to. It would be pretty convenient since they live in the ruins.