Human isotopic evidence from the Guanzhong Basin casts light on a century of agricultural and pastoral interactions at medieval metropolitan Chang'an during sixth century AD

The study investigates how agricultural and pastoral subsistence strategies intersected among elites and commoners in sixth-century Chang'an (Northern Zhou period), a time of intense interaction and hybridization between Han agricultural and non-Han (notably Xianbei and steppe) pastoral cultures. It addresses the debate over Han-ization versus Xianbei-ization by providing quantitative, scientific archaeological evidence of diet through stable carbon and nitrogen isotope analysis of human remains from nobles and commoners. The purpose is to reconstruct dietary variability, assess differences by social status and origin, and illuminate how shifting lifeways and identities were expressed through foodways in the capital region during a crucial transitional century.

Prior scholarship debates whether Northern Dynasties elites underwent Han-ization (adopting Han administrative and cultural practices) or whether Xianbei identity and culture were maintained and promoted (Xianbei-ization), with some arguing for multicultural hybridization. Archaeology has contributed limited quantitative data to this debate, though studies of burial elements suggest context-specific oscillations between Han and Xianbei features. Stable isotope analyses have previously been applied to Xianbei and related groups from Shanxi and Inner Mongolia (4th–5th c. AD), indicating shifts from pastoral/hunting to more agriculture following migrations into the Loess highlands and Central Plains. Syntheses of Chinese isotopic data show broad dietary patterns across regions and periods. However, isotopic analyses targeting high-status individuals (emperors, empresses, nobles) in the core metropolitan setting of medieval Chang'an have been lacking. This study fills that gap and situates new results within a compiled database (n=1233) spanning 550 BC–AD 1200 from 73 sites across northern China and neighboring regions.

Archaeological context: Samples derive from the Guanzhong Basin (modern Xi'an/Xianyang area), including eight noble and nine commoner individuals dated circa AD 500–600, plus three domesticated animals (sheep, cattle, horse) buried with Northern Zhou Emperor Wu (Yuwen Yong) and Empress A'shina. Noble tombs include the Xiao Mausoleum (Emperor Wu and Empress A'shina), the joint tomb of Princess Huihua (Tuyuhun) and General Qifu Xiaoda (Rouran), the tombs of Yuan Wei and Yu Yirong (Xianbei lineage nobles), Dugu Bin (Han lineage noble), and Li Yu (Sui official). Commoner remains come from Jichang II (n=6), Zhaijiasi (n=2), and Sunjianantou (n=1) cemeteries. Sampling and preparation: A total of 23 human skeletal samples were collected. Long bones (e.g., tibia, femur) were used to infer long-term diet; for select nobles, ribs/vertebrae were also analyzed to assess late-life diet (3–5 years pre-mortem). Collagen extraction followed Richards and Hedges (1999) with a final ultrafiltration step (Brown et al., 1988), then lyophilization. Isotope measurement: Analyses were conducted at the Environmental Stable Isotope Laboratory (ESIL), Institute of Environment and Sustainable Development of Agriculture, Chinese Academy of Agricultural Sciences (CAAS), using an IsoPrime 100 IRMS coupled with an Elementar Vario. Calibration used USGS40 and USGS41a; δ13C is reported relative to VPDB and δ15N to AIR with two-point calibration. Analytical precision was ±0.2‰ for both δ13C and δ15N. The three domesticated animal bones from the Xiao Mausoleum were analyzed at Beta Analytic (Miami, USA) with C/N (%C, %N, C:N) measurement; precision ±0.3‰ (δ13C) and ±0.5‰ (δ15N). Collagen quality was verified with C:N ratios between 2.9 and 3.6. Comparative dataset: The study compiled previously published human collagen δ13C and δ15N data (n=1233) from 73 sites across 12 geographic regions in northern China and adjacent areas (550 BC–AD 1200) to contextualize the Guanzhong results. Dietary interpretation thresholds used δ13C cut-offs at −18‰ (C3 vs mixed C3/C4) and −12‰ (mixed C3/C4 vs primarily C4).

- Animal baselines (Xiao Mausoleum): sheep δ13C −18.3‰, δ15N 5.5‰ (C3 grazer); cattle δ13C −11.9‰, δ15N 9.4‰; horse δ13C −11.2‰, δ15N 5.7‰ (both C4-based, millet-derived fodder). Cattle exhibited the highest δ15N among animals, suggesting more protein-rich/nutritious intake. - Noble diets (long bones): δ13C range −17.4‰ to −12.4‰ (mean −15.0 ± 1.5‰); δ15N 10.8‰ to 15.0‰ (mean 12.4 ± 1.4‰). Indicates predominantly mixed C3/C4 plant consumption with generally higher protein intake (meat/milk) among elites. - Commoner diets: Xi’an-area commoners (n=6) δ15N 8.5‰–9.5‰ (mean 9.1 ± 0.3‰); Baoji-area commoners (n=3) δ15N 8.8‰–9.7‰ (mean 9.1 ± 0.4‰). Mean δ15N difference between nobles and commoners ≈3.3‰, indicating substantially lower protein intake among commoners. Commoner δ13C spans −15.6‰ to −10.7‰ (mean −13.3 ± 1.4‰), reflecting both C4 (millet) and mixed C3/C4 (wheat/barley + millet) diets. - Intra-individual elite life-course changes (ribs/vertebrae vs long bones): Princess Huihua and Qifu Xiaoda show 13C-enrichment and lower δ15N in ribs vs long bones, indicating increased millet consumption and reduced protein intake later in life, consistent with adaptation to agricultural foodways at Chang’an. Emperor Wu and Empress A’shina vertebrae have lower δ13C than long bones, pointing to influence of C4-based proteins; slight δ15N decline in the emperor’s later life suggests reduced protein intake, while the empress shows slightly increased δ15N, implying continued preference for pastoral meat/dairy. - Regional comparative patterns (n=1233): Populations from Altai, Mongolian Plateau, Qinghai-Tibet, Tianshan-Pamirs show low δ13C and elevated δ15N (C3 grains + high animal protein; pastoral). Agricultural regions (Hetao, Longzhong, North Shanxi, Wei River Basin, Yanshan-Liaoning) show 13C-enriched and lower δ15N (millet-based, lower animal protein). Great Khingan, Russian Far East, and North China Plain show mixed C3/C4 with variable protein; many North China Plain individuals have relatively low δ15N, indicating crop-dominant diets. - Status and origin distinctions: Steppe-derived nobles (e.g., Princess Huihua −16.8‰, 14.1‰; Qifu Xiaoda −17.4‰, 15.0‰) exhibit C3-heavy, high-protein diets. Emperor Wu and Empress A’shina show more mixed millet–wheat/barley patterns (δ13C around −15.3‰ and −15.1‰; δ15N ~12.5‰–12.6‰). Lower-ranked Xianbei nobles (Yuan Wei, Yu Yirong, Li Yu) align more closely with Han nobles/commoners’ agricultural diets.

Stable isotope evidence reveals complex links between foodways, social status, and identity in sixth-century Chang’an. Elites had higher protein intake and diverse plant sources relative to commoners. Among elites, dietary signatures reflect origins and social trajectories: steppe-derived nobles retained pastoral dietary traits (C3 grains and high animal protein), while residence in the Guanzhong agricultural heartland fostered shifts toward millet and mixed C3/C4 consumption, with lower-ranked elites showing greater convergence with Han agricultural patterns. In married elite pairs, differences may reflect gendered status or personal preference (e.g., Princess Huihua’s higher δ15N than Qifu). The emperor and empress show convergent diets in Chang’an, consistent with textual records and elite integration. Commoners display broad δ13C variation indicative of mixed millet and wheat/barley agriculture, consistent with historical policies and supply requisitions emphasizing millet, alongside increased wheat/barley introduction to the Wei River Basin amid migrations and policy shifts. Integrating the Guanzhong data with the large comparative dataset underscores clear agro-pastoral vs agricultural isotopic clusters, demonstrating two-way interactions between pastoral and agricultural practices and identities. These findings support a nuanced, fluid model of Han/Xianbei hybridization operating differently across elite and non-elite strata, contributing to the sociocultural foundations that later characterized the Sui-Tang cosmopolitan milieu.

Quantitative stable isotope data from nobles and commoners in the Guanzhong Basin provide direct evidence for heterogeneous diets and status-linked differences during the sixth century AD. Xianbei (and related steppe) elites variably adopted agricultural foods, with some maintaining pastoral dietary features; lower elites appear to have shifted more markedly toward Han agricultural patterns. Commoners exhibit mixed C3/C4 agriculture, reflecting both migration-driven cultural exchange and policy influences. The study refines the Han-ization/Xianbei-ization debate by demonstrating multi-directional, status-contingent hybridization in foodways at Chang’an, informing understandings of how such interactions underpinned Sui-Tang developments. Future research should expand commoner sampling in the Chang’an area, particularly for Sui–Tang periods, and include comprehensive isotopic baselines from crops and animals to better resolve agricultural vs pastoral inputs and temporal dietary shifts.

Sample sizes for commoners in the immediate Chang’an area are limited, especially for Sui–Tang periods, constraining generalizability across time and social strata. The study also lacks extensive isotopic baselines from local crops and a broader range of domestic animals, which would improve source apportionment and refine interpretations of C3/C4 and protein contributions.