One pier with two stones: A case study on different stones used in the foundation of a Roman bridge

Perpira is a registered ancient bridge, probably constructed during the Late Roman/Early Byzantine, to span the banks of the Batman Stream. The foundations and the piers are the surviving remains of this bridge. Considering the current state, it is known that the bridge has not been repaired since it was discovered. Therefore, the remaining parts of the structure, especially the cut stone blocks, are original and contain precious information about the construction techniques and material selection of the period in which it was constructed. During the site investigations, it has been found that the stones used in the downstream and upstream sections may be different. In order to examine this unique application, samples were collected from the piers' downstream and upstream sections. The samples were then used to evaluate their petrographic, geochemical and engineering properties. At the macro scale, the questioned samples' petrophysical characteristics seem similar. However, the variances in their physicomechanical, petrographic, and mineralogical features indicate that they have distinctly different characteristics. The laboratory results demonstrate that the stone used in the upstream section is dolomite and has a strength of 25.21 MPa and a porosity of 25.38 percent, while the one used in the upstream section has a strength of 59.93 MPa and a porosity of 5.80 percent. According to the experiment results, it can be stated that Romans constructed this structure using highly competent engineering knowledge and material optimization. The findings also highlight how even a single piece of artefacts may provide new insights for understanding ancient material application practices.