Did you know... that beginning a sentence with an exaggeratedly large letter... such as the "D" to begin this paragraph, has a name. It's the Historiated Initial! It is discussed as such:
A historiated initial is an initial, an enlarged letter at the beginning of a paragraph or other section of text, that contains a picture. Strictly speaking, a historiated initial depicts an identifiable figure or a specific scene, while an inhabited initial contains figures (human or animal) that are decorative only, without forming a subject. Both sorts became very common and elaborate in luxury illuminated manuscripts. These illustrated initials were first seen in the Insular art of the early 8th century. The earliest known example is in the Saint Petersburg Bede, an Insular manuscript of 731–46, and the Vespasian Psalter has another.[1]
So here we see it's described as a method writers and artists used, Insular first seen in artwork in the 8th century.
