The plate of skull bone, sometimes as large as 5 cm (2 in) in diameter, would have been kept with the person until their death, serving as a charm or in some spiritual or religious capacity; burial of this bone plate was thought to return the body to its full state for the afterlife. Trepanning is amongst few surgical operations to be carried out in prehistoric times; other surgery was rarely undertaken; medicine men had neither the training or the specialised equipment required to do surgery on the internal body. The procedure would have taken around 60 minutes in a single session, and if done in several sessions, it could have taken up to 12 days to complete.