This research received financial support from the ERC Advanced Grant RurLand project (Rural Landscape in NorthEastern Roman Gaul, dir. M. Reddé) for stable isotopes analysis and a post-doctoral fellowship to M. Aguilera. Stable isotope analyses were performed at the SSMIM (Paris), with technical supervision by Joël Ughetto-Monfrin and Denis Fiorillo. We thank Jill Cucchi for copy-editing process. Olivier Blin gave us access to the faunal material from Palaiseau and Jouars-Pontchartrain. David Nicolas provided us a precious support in the search for faunal remains from Acy-Romance site. Crop fertility conditions in NorthEastern Gaul during the La Tène and Roman periods: a combined stable isotope analysis of archaeobotanical and archaeozoological remains.

While some consensus exists about the roles of southwestern China and northeastern India in the origin and diversification of the genus Citrus, the scarcity of its archaeological remains, as well as some methodological limits in unequivocally identifying taxa, do not facilitate reconstruction of the tempo and mode of spread of the genus towards other areas, notably the Mediterranean. Recent discoveries of archaeobotanical macro-remains (seeds and fruits) and pollen records from some important Italian sites in the Vesuvius area and Rome can be used to shed new light on this history. However, due to their morphological variability and the changes derived from the preservation processes, Citrus seeds appear difficult to recognise. In this paper, we present criteria to facilitate their precise identification, based on the observation of the morphology of modern seeds, and most of all the seed-coat patterns. The reference material consisted of "archaic" varieties of C. medica L. (citron), C. × limon (L.) Burm. f. (lemon) and seeds of C. × aurantium L. (bitter or Seville orange), C. × aurantiifolia (Christm.) Swingle (lime) and C. reticulata Blanco (tangerine, mandarin orange). Considering the fact that the general morphology of seeds, especially when mineralised, can confuse the identification of Citrus with Maloideae types, we also add criteria for the recognition of Cydonia oblonga Mill. (quince), Malus domestica Borkh. (apple), Pyrus communis L. (pear), Sorbus aria (L.) Crantz (whitebeam) and S. domestica L. (service tree). The observation of the keels and cell patterns was mostly useful to identify new material from Pompeii and Rome dating from the 3rd/2nd century b.c. and the Augustan period around the beginning of the Common (Christian) Era as C. medica L. (citron) and C. cf. × limon (L.) Burm. f. (possible lemon). The classical Greek and Latin sources helped us to understand the use and status of citrus fruits in the ancient world and, in combination with all available archaeobotanical remains compiled in this paper, have allowed us to discuss the spread of Citrus from its regions of origin to the eastern Mediterranean and then within the Mediterranean. © 2013 Springer-Verlag Berlin Heidelberg