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• CaCO 3 nanofibres have been found in recarbonated lime from archaeological sites. • Examples occur in UK and Latvia, with related nanosized material from Spain. • The nanofibres are typically 50 nm thick and have variable lengths. Calcium carbonate nanofibres have been described from a number of natural environments and have generally been found in similar locations to those of needle-fibre calcite, such as caves, palaeosols and calcretes. Here we report large amounts of calcium carbonate nanofibres in buried archaeological stratigraphy consisting of recarbonated lime from mortar or plaster. The materials were observed in Roman and medieval contexts and could have been associated with either manufacture or use of the lime products. The phenomenon appears to be widespread, occurring in examples from UK and Latvia, with related nanosized material from Spain. Possible mechanisms are discussed, but the reason for nanofibrous crystallisation occurring in these situations is not currently understood. [ABSTRACT FROM AUTHOR]