i taught a class on roman wax tablet books, as part of a series on historic books that jenny craig and i offered for several years, through the seattle center for book arts.
the wax tablet was employed for centuries as an affordable way to write casual communications, keep track of shipments, and make notations. the oldest known example was found in a 14th bce shipwreck off the coast of modern day turkey, nestled in the bottom of a jar of pomegranates. the romans popularized the structure with their constant need for cheap and portable writing material in their struggle to keep track of the taxes of the known world; however it continued to be used up into the middle ages.
several examples have been found containing secret messages embedded under the wax.