The Roman vicus of Eisenberg in Rhineland-Palatinate (Germany) has always been considered to be an important Roman iron smelting centre due to numerous slag finds and relicts of furnaces. Most excavations that revealed iron working debris have been performed in the nineteenth or early twentieth century. Their results and interpretations have been considered to be doubtful, but more recent excavations have brought to light further relics of iron working processes, which have not, however, helped to clarify the situation. Therefore, slag and ore fragments from two locations of discovery were selected for investigation, because no systematic investigations have been carried out on slags or other relics of iron working so far, despite the enormous importance of such a place. The first results of this investigation clearly prove the smelting of iron in slag-tapping furnaces during Roman times due to the morphology of the slag, but they also show that the metallurgical debris is obviously not in situ and has been used as filling material. In addition, the high-grade haematite ores also found on the ground could serve as a source for smelting.