Tablets of wood, or sometimes ivory, were used as writing surfaces in two ways: either ink was applied on them; or they were hollowed out and filled with wax so that one could write with a stulus. Along with the roll, the tablet was the principal writing vehicle during antiquity, being used for informal purposes, teaching, letters, drafting, and for records (such as letters of citizenship). The gradual substitution of sheets of parchment for wood or ivory may well have stimulated the development of the codex form. Tablets continued to be used into the twentieth century for informal financial accounts (by French fishermen, for example). During the Middle Ages, they fulfilled a variety of functions: drafting texts; trying out artistic designs; recording liturgical commemorations; note taking during study; accounting and legal contexts; as proto-Filofaxes; and as love tokens filled with amorous poetry. Tablets ranged in format from robust teaching tablets to portable girdle books. Although different colours of wax were used, black and green predominated. A number of tablets were sometimes bound together with leather thongs or within a leather case. Tablets were also made with handles (the tabula ansata), whose shape could serve as a decorative motif.