The term vitrified forts refers to remnants of stony fortifications of early iron age in which constituent rock fragments and boulders have been melted and/or welded together by heat, apparently in situ. Twenty source rocks and fifty glasses from eleven sites were analyzed. The conclusion is that no exotic rocks were used as flux nor were easily fusible materials selected. The builders appear to have used more sophisticated techniques that believed to ensure the durability of their constructions.