The contemporary decline in letter writing constitutes a huge cultural shift in the way society had communicated for centuries. Letters are among the earliest examples of writing in the history of humankind. Although the writing of letters was common during the classical period, it was not till the Middle Ages that the written letter became a central concern of rhetorical theory. Different things were achieved through the medium of letters. Besides being the main medium as administrative and clerical documents, letters are a very rich source ranging from church and state correspondence to social hierarchies and fiction. Furthermore, while medieval society, in general, was largely illiterate and rural, historians depend on the letters of ordinary people to create a picture of the past. Letter writing reached a peak between the fifteenth and twentieth centuries because of the availability of paper and also ease of travel and distribution by courier and the development of post.