All sorts of containers played an important role in the storage of food and dairy products in the economy of ancient Mesopotamia. Their importance is reflected, in particular, in the proto-cuneiform writing system. The representation of containers in early writing usually coincides with the use of so-called 'frame signs'. Frame signs can be considered a subgroup of graphemic classifiers, and in some sense they can be described as mensural classifiers according to Alexandra Aikhenvald's study of noun classification. Although frame signs such as these can occur independently, they usually include other graphemes, which are inscribed in the blank space.