King Eric XIV of Sweden (1533–1577) is known for his dramatic life: he was deposed and imprisoned in 1568, allegedly became insane, and was murdered by the new king, his brother. But Eric was also very well versed in languages, music, history, art, astrology … He owned a library of over 200 volumes. Four of them still survive, of which two are Neo-Latin historical works: Johannes Magnus’ Historia de omnibus Gothorum Sueonumque regibus (Rome 1554) and Marcantonio Sabellico’s Enneades (Basel 1538). In the margins of these two works, King Eric wrote a few comments, but, more importantly, he also drew small images in the margins: hearts, axes, sceptres, swords, books, crowns, and so forth. The pictures are normally found next to underscorings in the text, and they recur time and again next to underscorings with a similar theme. Each picture thus corresponds to a given theme, of which they are symbols. Taken together, they constitute a system that facilitates easy retrieval of important and interesting material, reminiscent of a commonplace book. The aim of this paper is to explain how this system worked, and so to throw light on how two Neo-Latin works were understood by a contemporary reader.