Revealing archaeological olive diversity: insights from stone geometric morphometrics, experimental charring, and varietal identification (Port-la-Nautique, France, Roman period)

Abstract

The cultivated olive tree, domesticated in the Levant by the mid-5th millennium BCE, spread westward across the Mediterranean to reach southern France by 600 BCE. Although geometric morphometrics applied to archaeological olive stones has provided insights into this diffusion, morphotype identification remains challenging, and the effects of charring, the most common preservation mode, are poorly understood. We compared ten morphometric approaches to determine the most effective method for discriminating wild and domesticated morphologies and distinguishing varieties. Controlled charring experiments assessed the effects of temperature, duration, and atmosphere on stone morphometry. The resulting methodology was applied to 261 olive stones from the Roman villa of Port-la-Nautique and the Capelles fishpond (Narbonne, France). Elliptic Fourier Transforms proved most effective for taxonomic discrimination, and charring up to 350°C did not prevent reliable classification against modern uncharred references. This approach enabled the identification, for the first time, of archaeological stones resembling present-day varieties, offering new insights into the evolution of olive agrobiodiversity.