When you write in the margin of a book, you join a practice that reaches back to the ancient librarians of Alexandria and forward into the highlighted passages of your e-reader. Marginalia—readers' notes, symbols, and drawings added to texts—has never been one activity. In the medieval era it served scholarship and decoration alike; during the Renaissance and the Printing Revolution it became a systematic tool of intellectual conversation; by the 19th century it had acquired its very name and a reputation for personal reflection. I want to walk you through that evolution, because what changed in each era was not just how people annotated, but what readers believed a book was for.

The Enduring Practice of Marginalia: A Historical Overview

One of the earliest forms of marginal commentary was the scholion—a written note placed in the margin, typically supplied by the scribe who produced the manuscript copy. Even earlier, three Greek Homeric scholars who successively served as librarians at the Library of Alexandria—Zenodotus of Ephesus, Aristophanes of Byzantium, and Aristarchus of Samothrace—developed a system of symbols for marking up Homer's poetry in the margins. That system, named after the obelus (the ancestor of the modern dagger †), became known as obelism. So annotation is, from its beginnings, a scholarly act: a way of flagging, questioning, and interpreting a text from the outside edge inward.

What makes marginalia so durable, though, is its variety. As Kiri Wagstaff observed in a 2012 paper on the evolution of marginalia, readers have added marginal commentary "for a variety of personal and public purposes," and historians have mined the annotations of important figures to observe their sometimes raw, immediate responses to texts. That dual character—the private scrawl and the public scholarly apparatus—is the thread that runs from medieval parchment to the digital page.

Medieval Manuscripts: Scholarly Notes and Playful Art

In the medieval manuscript, the margin was not dead space; it was working space. Des Cowley and Anna Welch, librarians of the History of the Book at the State Library Victoria, describe marginalia as a historic practice embedded in the manuscript tradition itself, where the border could hold commentary, correction, or artistry as part of the page's design.

A Bodleian Library manuscript (MS Douce 322) offers a vivid example of how scholarship and decoration blur. The page carries a large decorated initial S, adorned with spray vines that extend along the gutter and curve around the corners of the text—an ornamental style typical of its period in English manuscripts. But look closer at that initial: along the left side run curved flourishes resembling the letters nō stacked vertically. These closely resemble the standard abbreviation for nota—as in nota bene, "note well"—the scribe's signal to mark an important passage. A mark of scholarly attention was folded into the decoration itself.

Yet not every medieval margin image was so earnest. In recent decades, scholars have made many efforts to analyze marginalia in illuminated manuscripts, and multiple theories persist about its function and meaning in context. One study of medieval and Renaissance manuscripts depicting snails in the margins suggests the illustrations functioned as comic relief, playing on the similarity between knights' armor and snails' shells. Other studies indicate marginalia was used to provide additional commentary and support for the surrounding text. Humor, emphasis, and explication could share the same page—and literate audiences of the time would have recognized all of them.