A recent re-examination of the architectural and other sculpted stone fragments from Silchester (Calleva Atrebatum) drew attention to the small sandstone column on which is scored an ogham inscription. The commonest materials used for columns, capitals and ornamental sculpture at Silchester are the fine Jurassic limestones of Bath or Portland type. A very few pieces are carved intertiary sandstones or imported marble. This is the pattern for architectural masonry throughout southern England in the Roman period; limestone predominates and sandstone, usually greensand, is rare. On visual examination the particular stone with the ogham appears to be different from that of the other architectural fragments in the Silchester collection. It should also be noted that no similar material has so far been identified in the city wall or amongst any of the other ordinary building materials recovered from the Roman town. On the basis of visual examination alone it has been suggested that the stone originated from the calcareous grit of the Oxfordshire Corallian (Boon 1959, 87), but doubts about this identification led us to a more searching investigation to ascertain the character and source of the stone. Before introducing these analyses and their results it will be useful to summarize our present knowledge of the Silchester ogham. In this way the implications of the new results can be more satisfactorily appreciated.