Paleogenomic evidence for genetic heterogeneity and prior admixture in Gothic-associated communities of late antique Bulgaria.

We report genome-wide ancient DNA from 37 individuals retained after conservative archaeological and genomic reassessment of 53 screened samples from two Gothic-period mortuary contexts in present-day Bulgaria: the Aquae Calidae necropolis in Thrace (n = 20; c. 320 CE-375 CE) and the Aul of Khan Omurtag (AKO) in Moesia Secunda (n = 17; c. 350 CE-489 CE). The filtering process excluded individuals with uncertain or probably later-medieval horizon assignment, including a C5-area component linked by READv2 kinship to suspected later-horizon burials. We evaluate three non-exclusive models for Balkan Gothic formation, namely, migration-continuity from northern and Pontic Gothic horizons, a Wenskus-Wolfram-Pohl tradition-bearing cultural-political formation model across changing demographic substrates, and the Roman frontier formation. The two assemblages share Gothic-associated material culture and Christian east-west burial orientation, but they are not a single genome-wide population. Proximal qpAdm models distinguish a southern Anatolian/Marmara-related and northern/Pontic structure at Aquae Calidae from a simpler Chernyakhov-related and Balkan Late Antique structure at AKO. f4 statistics further show that the Anatolian-related component at Aquae Calidae cannot be explained solely as a Chernyakhov-carried signal. DATES places north-south admixture at approximately 12.44 ± 2.36 generations before burial (Z = 5.26), consistent with a pre-burial ancestry mixture rather than a single intact Gothic migration. Kinship is confined within sites. Together, the data reject a single biological Gothic population moving unchanged into the Balkans and instead support a formation process combining migration, multiethnic coalition, and frontier incorporation.