This work investigates the use of Old Red Sandstone from South Wales, Gloucestershire, Avon and Somerset during the Roman period, for rotary querns. It is based on detailed petrographic studies of these rocks at both microscopic and macroscopic levels to define practical keys which allow types of Old Red Sandstone, and hence artefacts made from it, to be identified and provenanced to their geological formations. 1200 rotary querns of Old Red sandstone from 180 sites were analysed (stretching from southeast Wales in the west, to Bedfordshire and Cambridgeshire in the east. It extends as far south as Dorchester (Dorset) and as far north as Coleshill (Warwickshire)). The petrological study also identifies the three major source areas in the Roman period as the Forest of Dean, the Bristol area and the Mendips and investigates the differences in the distribution of finds from each of these sources. A typological study is included, with a detailed description and analysis of the types of ORS querns manufactured, their dating and their distribution. The routes and mechanisms through which the querns were moved are also investigated and the production of ORS querns is also assessed.