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Large-scale medieval urbanism traced by UAV–lidar in highland Central Asia

Nature volume 634, pages 1118–1124 (2024)Cite this article

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Abstract

Aerial light detection and ranging (lidar) has emerged as a powerful technology for mapping urban archaeological landscapes, especially where dense vegetation obscures site visibility1,2. More recently, uncrewed aerial vehicle/drone lidar scanning has markedly improved the resolution of three-dimensional point clouds, allowing for the detection of slight traces of structural features at centimetres of detail across large archaeological sites, a method particularly useful in areas such as mountains, where rapid deposition and erosion irregularly bury and expose archaeological remains3. Here we present the results of uncrewed aerial vehicle–lidar surveys in Central Asia, conducted at two recently discovered archaeological sites in southeastern Uzbekistan: Tashbulak and Tugunbulak. Situated at around 2,000–2,200 m above sea level, these sites illustrate a newly documented geography of large, high-altitude urban centres positioned along the mountainous crossroads of Asia’s medieval Silk Routes (6th–11th century CE (Common Era)4,5. Although hidden by centuries of surface processes, our pairing of very-high-resolution surface modelling with semiautomated feature detection produces a detailed plan of monumental fortifications and architecture spanning 120 ha at Tugunbulak, thereby demonstrating one of the largest highland urban constellations in premodern Central Asia. Documentation of extensive urban infrastructure and technological production among medieval communities in Central Asia’s mountains—a crucial nexus for Silk Road trade networks6—provides a new perspective on the participation of highland populations in the economic, political and social formation of medieval Eurasia.

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Fig. 1: Location of study sites.
Fig. 2: Lidar mapping of Tugunbulak.
Fig. 3: Lidar mapping of Tashbulak.
Fig. 4: Lidar and crest line mapping of sector A, Tugunbulak.
Fig. 5: Comparison of GPR and lidar crest lines at Tashbulak.

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Data availability

All relevant data are provided with the paper and its Supplementary Information. The datasets used to calibrate all radiocarbon dates are available in Supplementary Table 3. An abridged lidar dataset required to execute crest line analysis and correlation and validation analyses is openly available at GitHub (https://github.com/JasonLiu2024/high-resolution-lidar-traces-large-scale-medieval-urbanism).

Code availability

All code required to execute crest line analysis and correlation and validation analyses is openly available at GitHub (https://github.com/JasonLiu2024/high-resolution-lidar-traces-large-scale-medieval-urbanism).

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Acknowledgements

The 2022 fieldwork at Tugunbulak was funded by the National Geographic Society (PI-Frachetti). The drone and lidar equipment were provided by a grant from the McDonnell Center for the Space Sciences, Washington University in St. Louis (co-PI, Frachetti). Since 2023, the project has been codirected by M. Frachetti, F. Maksudov and S. Mehendale, with onward funding provided by the Tang Center for Silk Road Studies and the Society for Archaeological Exploration of Eurasia. Special thanks to the former Ambassador of Uzbekistan, J. Vakhabov, and to A. Burkhanov (Ministry of Foreign Affairs, Uzbekistan), for facilitating drone permissions.

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Authors and Affiliations

  1. Spatial Analysis, Interpretation & Exploration (SAIE) laboratory, Department of Anthropology, Washington University in St. Louis, St. Louis, MO, USA

    Michael D. Frachetti, Jack Berner & Xiaoyi Liu

  2. Department of Computer Science and Engineering, Washington University in St. Louis, St. Louis, MO, USA

    Xiaoyi Liu & Tao Ju

  3. Department of Anthropology, Colorado State University, Fort Collins, CO, USA

    Edward R. Henry

  4. National Center of Archaeology, Uzbekistan Academy of Sciences, Tashkent, Uzbekistan

    Farhod Maksudov

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  1. Michael D. Frachetti
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Contributions

M.D.F. and F.M. conceptualized the study. M.D.F., F.M. and E.R.H. collected the data. M.D.F. and T.J. designed the methodology and analysis, with input from F.M., J.B. and X.L. M.D.F., J.B., X.L., E.R.H. and T.J. carried out the analysis. M.D.F. and J.B. wrote the initial draft, and all authors contributed to writing and editing of the final manuscript.

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Correspondence to Michael D. Frachetti.

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Nature thanks Nicola Di Cosmo, Roland Fletcher, Simone Mantellini, Andreas Mayr and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.

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Extended data figures and tables

Extended Data Fig. 1 Panoramic photos of study sites.

a) Tugunbulak, view east and b) Tashbulak, view northeast. Photos by M. Frachetti.

Extended Data Fig. 2 Detail lidar and crestline mapping, Tashbulak.

a) Very high resolution (VHR) lidar surface of Tashbulak, hill-shaded with 2x vertical exaggeration; b) Weighted crest line feature mapping of Tashbulak; c) detail of main structural area (hill shaded topography with crest lines); d) detail of southern extent of site showing outer wall features (hill shaded topography with crest lines).

Extended Data Fig. 3 Radiocarbon chronology, Tugunbulak.

Preliminary calibrated date ranges of AMS radiocarbon samples from Tugunbulak (sector A, excavations 2022). (For dates and calibration data, see Supplementary Information, Table 3).

Extended Data Fig. 4 Lidar and crestline mapping, Tugunbulak sector B.

a) Detail of lidar surface of sector B, Tugunbulak (hill-shaded with 2x vertical exaggeration) b) Weighted crest line feature mapping of sector B, Tugunbulak.

Extended Data Fig. 5 Lidar and crestline mapping, Tugunbulak sector C and D.

a) detail of lidar surface of sector C, Tugunbulak (hill-shaded with 2x vertical exaggeration); b) weighted crest line feature mapping of sector C, Tugunbulak. c) Detailed lidar surface of sector D Tugunbulak (hill-shaded with 2x vertical exaggeration). d) Weighted crest line feature mapping of sector D, Tugunbulak. Note: adjusted parameters for crest line rendering in these images are d = 11 (mesh depth) and n = 4 (neighborhood) (see Methods).

Extended Data Fig. 6 Correlation and hit rates of Tugunbulak manual tracing and crest lines.

Results of confusion matrix and spatial correlation (hit rates) between visually drawn features and semi-auto detected crest lines in selected polygon at Tugunbulak (Blue = hits, Red = miss). Correlation radii shown at .9 m and 1.4 m.

Extended Data Fig. 7 Correlation and hit rates of Tashbulak GPR and crest lines.

Comparative results of confusion matrix and spatial correlation (hit rates) between GPR centerlines and semi-auto detected crest lines in main area of architecture at Tashbulak, (Blue = hits, Red = miss). Correlation radii shown at 0.8 m, 1.0 m and 1.2 m.

Extended Data Fig. 8 Detailed view, Tashbulak GPR and crestline correlation.

Detailed view of correlation between GPR centerlines and semi-auto detected crest lines in two focal areas of architecture at Tashbulak. (Blue = hits, Red = miss). Correlation radius shown at 1.0 m.

Supplementary information

Supplementary Information

Supplementary information, including Figs. 1–10 and Tables 1–4.

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Frachetti, M.D., Berner, J., Liu, X. et al. Large-scale medieval urbanism traced by UAV–lidar in highland Central Asia. Nature 634, 1118–1124 (2024). https://doi.org/10.1038/s41586-024-08086-5

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