Climate, human settlement, and migration in South Asia from early historic to medieval period: Evidence from new archaeological excavation at Vadnagar, Western India

Between the second urbanisation of late Iron Age/Early historic and medieval period Indian subcontinent experienced repeated invasion/human migration of central Asian warriors from Greco-Bactrian conquests till Sultanate-Mughals of sixteenth century. Historians often argue whether such invasions/migrations in the past were driven by change in climate and/or social dynamics. We present results of first detailed archaeological excavation and chronology from a multi-cultural site of Vadnagar, Gujarat state, Western India. We document records of seven cultural stages of continuous human settlement from ca. 2754 calibrated (cal) years B.P. (contemporary to Late-Vedic/pre-Buddhist Mahajanapadas or oligarchic republics), Mauryan, Indo-Greek, IndoScythian or Shaka-Kshatrapas (AKA 'Satraps', descendants of provincial governors of ancient Achaemenid Empires), Hindu-Solankis, Sultanate-Mughal (Islamic) to Gaekwad-British colonial rule (-318 years B.P.) and recent. We constrain the climate (Indian summer monsoons or ISM) at Vadnagar by both bulk and isotope sclerochronology (seasonality) of molluscan shells and show that each of these periods flourished during a good ISM phase. Conversely, the arid/hyper-arid phases witnessed decline in material culture, craftsmanship, and/or increased social instability yet the settlement was never abandoned thus making Vadnagar the oldest living city within a single fortification unearthed so far in India. We also compare the proxy climate data with the coupled General Circulation Climate (Earth system) model-generated precipitation over western India that is in antiphase with Arid Central Asia (ACA). We suggest that the seven major phases of invasions/migration to India over the past 2200 years occurred during periods when the ACA was hyper-arid and uninhabitable, but the agrarian subcontinent was prosperous with relatively stronger ISM.