Bayesian archaeoseismic chronology of the Stratonikeia Frigidarium from construction to seismic collapse

Abstract

The absolute chronology of the Frigidarium of the Roman Bath complex at Stratonikeia, southwestern Türkiye, is established through optically stimulated luminescence dating of brick, mortar, and quartz-rich sediment. Five specimens were dated under a fully documented dose-rate protocol that includes grain-size-dependent attenuation, a carbonate water-equivalence correction for lime-bound mortars, and an explicit assessment of gamma dose-rate heterogeneity. The OSL ages were synthesized in a constrained Bayesian phase model carrying only stratigraphic and terminus post quem priors. Three phases emerge in the building’s life cycle. Primary construction is placed in the late first to early second century CE, with a posterior median of 162 CE and a 95.4% highest-posterior-density interval of 60–323 CE. A repair episode follows at a mode of 375 CE within 365–499 CE, consistent with restoration after the 365 CE Eastern Mediterranean earthquake. Gamma-field geometry is treated as a Bayesian nuisance parameter, propagating compound-masonry dosimetric uncertainty into the phase posteriors. Under dosimetric priors alone the collapse dates to a mode of 545 CE within 405–802 CE, spanning the 494, 554 to 558, and circa 610 to 630 CE seismic anchors without discriminating among them. Coins minted in 613 CE and sealed beneath the collapse debris narrow the collapse window to 613–850 CE with a mode of 633 CE; the circa 610 to 630 CE window then dominates, with overlap probability 0.31 at a 25-year tolerance, supporting a seismic trigger for the terminal loss of monumental function in the early seventh century CE.