Fig 1.
Map of the study area and location of archaeological sites.
The study area is located south of the river Danube in the present German state of Bavaria. The region includes the part of Roman Raetia II that later became part of the first tribal duchy of the Baiuvarii. The Limes, the Roman-Germanic border established in the 1st century AD, was abandoned in the middle of the 3rd century, and the river boundaries of the Rhine, Iller, and Danube became the new imperial borders. Archaeological sites in the border zone: 1 Burgweinting A and B (BWA, BWB), 2 Irlmauth (IRM), 3 Alteglofsheim (AEH), 4 Straubing-Bajuwarenstraße (STB). Archaeological sites in the hinterland: 5 Altenerding (AED), 6 Munich-Perlach (PEL), 7 Unterhaching (UTH). (Map data: WMS Digital Terrain Model https://gdz.bkg.bund.de/index.php/default/wms-digitales-gelandemodell-gitterweite-200-m-wms-dgm200.html), Data licence Germany–attribution–Version 2.0 and GeoBasis-DE / BKG (2022) [7, 8]. Boundaries of provinces and course of the Limes shown as displayed in Harbeck et al. [9], dukedom drawn as displayed in Grollmann et al. [10]), (created with QGIS 3.18.3 Zürich).
Table 1.
Archeological sites investigated in this study.
Fig 2.
Geological maps of the study region.
Only the main geological units are named (Illustration: QGIS, map base GK1000 © BGR Hannover (2014) [60]. Left (A) and Right (C) Corresponding details. Grey: Location and median of strontium values of the reference data. Red circles: 10-km radii (2x5 km) around the archaeological sites (overlapping for two sites). This resulted in four regional groups: Regensburg (REG, with Burgweinting, Irlmauth and Alteglofsheim), Straubing (STB), Erding (AED), and Munich (MUC, with Munich-Perlach and Unterhaching). Center (B) Geological map of Bavaria and locations of archaeological sites: 1 Burgweinting A and B (BWA, BWB), 2 Irlmauth (IRM), 3 Alteglofsheim (AEH), 4 Straubing-Bajuwarenstraße (STB), 5 Altenerding (AED), 6 Munich-Perlach (PEL), 7 Unterhaching (UTH). (created with QGIS 3.18.3 Zürich).
Fig 3.
Local ranges and distribution of 87Sr/86Sr values per region and site.
(A) Region Straubing (STB), (B) Region Regensburg (REG), (C) Region Erding (AED) and (D) Region Munich (MUC). 87Sr/86Sr (y-axis) of samples from predefined study region divided into groups (x-axis): env = environmental samples, animE = animal enamel, humE = human enamel, humEInf = human enamel of infans (0–12 years), B = bone (animal or human) (followed by an r = part of the reference data set, no r = archaeological site investigated). Red area: calculated range of bioavailable strontium based on all biomineral samples of the region. Symbols provide a chronological classification. Numbers = grave numbers of individuals from which both bone and enamel were measured. If values from environmental samples were known from the literature, they were added for comparative reasons: Lengfelder et al. [112]: soil, vegetation, water for AED and MUC, Hoogewerff et al. [113]: soil for REG, Neumann et al. [114]: soil and snail MUC. Right side: Distribution of samples separated by reference and respective site: Straubing (STB): N = 217, Regensburg (REG): N = 80, Erding (AED): N = 78, and Munich (MUC): N = 76 (illustration: R with packages ggplot2 [115, 116], ggbeeswarm [117], ggside [118], ggrepel [119]).
Table 2.
Characteristics of assumed newcomers according to deviating isotopic ratios or presence of ACD.
Fig 4.
Circular charts illustrating the proportion of non-locals (A) in gender groups (females vs. males), (B) in settlement zones (border vs. hinterland), (C) for archaeological sites (VW Burgweinting, IRM Irlmauth, STB Straubing-Bajuwarenstraße, AED Altenerding, PEL Munich-Perlach, UTH Unterhaching). Given numbers are frequencies of all non-locals, whose strontium values are found outside the range of their burial region, which summarize the frequencies of individuals who show strontium ratios outside the local range of the Northern Alpine area in South Bavaria (filled in dark red) and individuals whose strontium values are found in other study regions in South Bavaria (filled in grey). (Map data: see Fig 1). (created with QGIS 3.18.3 Zürich and Excel).
Fig 5.
Minimum Frequency of Migrants (MFM) in different periods.
Late Neolithic N = 108, Early Neolithic N = 82, Early Bronze Age N = 59, Iron Age N = 24, Late Antique N = 109, around 500 AD N = 108 and Early Middle Ages N = 37. Error bar = confidence interval, red line = mean frequency of immigrants if all periods are considered together, red box = confidence interval for this average.
Fig 6.
Variability of carbon and nitrogen isotopic ratios.
Scatter plots of δ13C and δ15N values of human bone collagen: Straubing-Bajuwarenstraße (STB, N = 33), Burgweinting, Irlmauth and Alteglofsheim (BW+IRM+AEH, N = 49) in the border zone, and Altenerding (AED, N = 44), Munich-Perlach and Unterhaching (PEL+UTH, N = 29) in the hinterland. Mean values and standard deviations (SD) are based on postweaning individuals (excluding infans I children = values outlined in orange) and were calculated using SPSS. Red lines represent 99% HDIs (calculations: hdr.den function of R package hdrcde [99]) (illustration: Excel).
Fig 7.
Differences between bulk dentine and bone collagen.
(A) Differences between bulk dentine and bone collagen of individuals without notable attributes (N = 11, illustrated in green), and (B) individuals with notable attributes (outliers in enamel 87Sr/86Sr illustrated in blue, outliers in bone collagen δ13C and/or δ15N illustrated in red, or the presence of ACD illustrated in orange) (illustration: Excel).
Fig 8.
Stable carbon and nitrogen isotope profiles of six selected females (AED_105, AED_343, BWA_10071, BWA_10075, BWA_10254*, PEL_12).
δ13C (blue shades) and δ15N (red shades) values of collagen from incremental dentine serial sections of molars (M1-M3) and bone collagen (square). Error bars represent the putative timespan each datapoint covers. Dotted lines represent common dietary signals at burial sites (99% HDIs) (illustration: Excel).