They were known to Pliny the Elder as 'oculi', or eyeballs, due to their rounded appearance as a consequence of being melted. They were made by slicing small sections of canes (c.5 - 10 mm thick), arranging them on a surface such as a terracotta tile and reheating them in a furnace until they deformed under the influence of gravity, resulting in a flattened, rounded 'button' shape. The underside may have needed grinding to remove any particles of clay that may have stuck to it.
The use of purpose-made counters for board games was a Roman introduction to Britain where gaming was clearly important. A 24 year old man from Lullingstone villa was buried in AD300 with his gaming board and 30 gaming piece (15 red and 15 white) so that he could play eternally in the afterlife.