The creation of meaning in texts requires the use not only of the verbal but also of the visual way, while understanding the text needs to understand the messages expressed verbally and visually, such as photographs, diagrams, charts, maps, sketches play a significant role.
Kalantzis, M. & Cope, B. (2001) Πολυγραμματισμοί (Multiliteracies)
Kress and van Leeuwen have noted that visual communication is becoming so critical in the field of public communication, that inevitably attracts visual literacy is not just social approval, but is now a matter of survival. To learn to understand texts essentially means learning to "read" verbal and visual messages.
In its most basic sense, multimodality is the mixture of textual, audio, and visual modes in combination with media and materiality to create meaning. The collection of these modes, or elements, contributes to how multimodality affects different situations, or opportunities for increasing an audience's reception of an idea or concept. Everything from the placement of images to the organization of the content creates meaning.
Lutkewitte, Cl. (2013). Multimodal Composition: A Critical Sourcebook. Boston: Bedford/ St. Martin's.
While multimodality as an area of academic study did not gain traction until the twentieth century, all communication, literacy, and composing practices are and always have been multimodal.
Kress, G. (2010). Multimodality: A Social Semiotic Approach to Contemporary Communication. New York: Routledge.