## 1 Introduction  
The iron slag samples investigated in the present study were unearthed at three major archaeological sites located on the Eastern frontier (_limes_) of Roman Dacia, in today Mures County, Romania (Figure 1). At Brancovenesti (Hungarian name: Marosvecs) and Calugareni (Mikhaza), the remains of the Roman auxiliary forts and the adjacent military settlements are known since the 18 th and 19 th century.  
The fortlet (watchtower) identified at Vatava (Felsorepa) during a field survey in 2011 is supposed to be closely linked to the Brancovenesti fort. Relying on the natural protection offered by the nearby mountains and hills, the defensive structures of the eastern _limes_ controlled the main traffic routes towards the _barbaricum_. The Brancovenesti fort, assisted by watchtowers, monitored the border section towards the upper Mures Valley (Felso Maros-mente), whilst the Calugareni fort supervised the upper Niraj Valley (Felso Nyarad-mente). In the 2 nd and 3 rd centuries centuries AD, both forts were strategically important military locations of the eastern border of the Dacian provinces.  
During the research excavations carried out at Brancovenesti and Calugareni, in the military forts and the adjacent settlements (_vici_) as well as at the watchtower from Vatava, plenty of Roman material was recovered, mainly ceramic vessels, building materials and animal bones, but also stone, bone, glass, iron and copper alloy artifacts. At each location, rich iron slag deposits have been found; at Vatava, even some blacksmithing tools have been recovered [1; 2; 3; 4]. The multitude of the iron slags indicate the presence of some kind of metallurgical workshops; however, up to now, neither smelter (furnace) nor smithery remains weren't discovered, so presently the exact whereabouts of the presumably practiced activity is unknown.  
Knowledge on the slag finds' chemical-mineralogical composition and their microstructural analyses could enable to identify the remains as smelting byproducts or primary/secondary smithing debris. The value of the Fe\({}^{3+}\)/Fe\({}^{2+}\) ratio, defined mainly by the redox condition evolved during each particular stage of processing, could allow us to conclude if iron-producing or iron-working took place at either location.  
The present study is focused primarily on the elemental analysis of the slag samples. Chemical composition was determined by PXRF (Field Portable X-ray Fluorescence Spectroscopy) and ICP-MS (Inductively Coupled Plasma Mass Spectrometry). In addition, structural-mineralogical investigation of selected samples was carried out by PXRD (Powder X-ray Diffraction) and FTIR (Fourier Transform Infrared) spectroscopy, and the Fe\({}^{3+}\)/Fe\({}^{2+}\) ratio was determined using EPR (Electron Paramagnetic Resonance) spectroscopy measurements. The information acquired facilitate the categorization of the finds and could shed some light on the nature of the metallurgical activity practiced  
Figure 1: Roman fortifications on the eastern Dacian limes on today Mures County (©© Szabo Mé Mé).  
at the archaeological sites in question (iron production, refining or processing), the metallurgical techniques used, and on the closer provenance or more distant sourcing of the raw materials used [5; 6; 7].