Habarcsok a Keszthely-fenékpusztai késő római erődből: a petrográfiai-geokémiai és mérnökgeológiai vizsgálatok eredményei [Mortar samples from the Late Roman fortress of Keszthely-Fenékpuszta: results of petrographic-geochemical and engineering geological analyses]

The Roman fortress of Keszthely-Fenékpuszta, built in the 4th century AD, was located at the western edge of Lake Balaton on a peninsula bordered by open water and marshy peat bogs. The well-protected fortification played a significant infrastructural role, due to the fact that the lake could be crossed here along a main north-south road of Pannonia. Archaeological excavations started in 2009 had the primary goal to clarify the location, floor plan and dating of individual buildings (nos. 24, 25 and 27). Based on petrographic, geochemical, and engineering geological investigations of mortars used in the constructions, we were able to gain insight into the possibilities of answering certain archaeological questions with geoarchaeometric methods. Mortar samples were systematically collected from the different locations representing the functions and construction phases. Based on the archaeological research three chronological groups (I.-III: end of 3rd c. to early 7th c. AD) were distinguished; two of them belong to the late Roman Period (I.-II.) and one (III.) to the Migration Period. The aggregates of the mortars were analyzed by polarized light microscopy and thermoanalytical method. The chemical examination of the binder was carried out by scanning electron microscopy. Additionally, water absorption, density and compressive strength of the mortars were also determined. Based on the results, we can conclude that the mortars of all three periods are of air lime nature containing Mg and Si impurities and both the binders and additives were produced using local raw materials rich in dolomite components. The higher compressive strength values of the mortars of the 3rd period (late 5th to early 7th c. AD) are probably due to the slightly different composition of the binder, or they can also be explained by the static role of the selected pillars. © by the author(s)