What are commentaries?

A commentary is a resource (usually a book) that a scholar can use while reading an ancient text to better understand the work on a grammatical, interpretive, and analytic level. They can be aimed at any level of user, from someone just starting to read an ancient language to professional academics, but they usually share most of the same elements: an introduction, the text in Latin, Greek, or another language, notes on the text, and a bibliography. Classicists will refer to the whole book as a commentary, but the notes section is really what they mean: this is the heart of a commentary