This piece belongs to a group of caskets, which are containers for holy relics. Small in size, they are made of slate stone or metamorphic rock (schist).Considered sacred and venerable, relics were placed inside stupas to commemorate the demise of important Buddhist teachers. Buddha's relics have also been placed inside several such caskets. After cremation, bones, teeth and hair are saved and honoured by erecting a stupa over it.In western Indian Buddhist cave temples and in the Gandhara region, many stupas in different shapes containing the holy relics of Buddhist teachers have been constructed or carved.Stupas represent the 'nirvana' of Buddha. Pious devotees would circumambulate them, remembering the passing of Buddha.