Homer and other poetical texts were used in school rooms during the classical period, and after. Inevitably this led to a need for explanation of unusual or obsolete words, summaries of books, and explanations of mythological events — the same sorts of things that modern students seem to require in order to read Jane Austen or Shakespeare.
Ancient texts were written on papyrus rolls or scrolls. These had narrow columns, and narrower margins. It was possible to place a letter or symbol in the margin, but little more, although we do have examples of attempts to write in margins. Consequently these explanations had to be written in separate rolls.
These commentaries were composed early in the classical period, and continued to be composed and compiled throughout antiquity. They often consisted of a series of entries, beginning with the word or words under discussion, or the beginning of the line of poetry concerned, or the start of the first line of a passage, followed by the comments. These comments would often include comments from older commentators, often separated by “allws” (“alternatively”).
Inevitably such commentaries could swell to a considerable size, and might therefore be epitomised in turn, and then the epitome augmented. Copyists might feel able to change the comments, far more than with a normal literary text. Many of the commentaries are lost, subsumed into subsequent compilations of comments, but a considerable number survive.
In the Hellenistic period, at the museum of Alexandria, the staff worked on the text of Homer and other classical texts, producing considerable quantities of commentary on textual and other issues. None of this material has survived directly, as stand-alone commentaries — our earliest extant commentaries are 2nd century BC — but they are quoted again and again in subsequent compilations.
The invention of the modern book form — the parchment codex — made a considerable change to the practice in this area. A codex could contain considerably more text than a papyrus roll, and nearly all codices have wide margins. It was therefore perfectly practicable to take material from commentaries and write it in the margin; and this practice seems to have become endemic at some period between the 4-6th centuries AD, and continues down to the end of the Byzantine period of Greek texts.
These marginal comments are known as “scholia”, although in some branches of classical studies the term is also applied to the stand-alone commentaries, which, after all, contain the same sorts of material and are usually the sources of the scholia.
The “old scholia” were soon supplemented by Byzantine scholia. These themselves were often based on older sources, directly or indirectly, and therefore can preserve ancient opinion about ancient texts.
A thorough introduction to the subject, and what commentaries and scholia exist for classical Greek texts, with references, can be found in Eleanor Dickey’s Ancient Greek Scholarship, which I thoroughly recommend and which is the source for these remarks. She also details how to read a critical edition, the Latin abbreviations used, and gives exercises in how to read and translate scholia. And the book is very cheap as well! Anyone with an interest in the subject should buy one.
I am amused to see Cramer editing various scholia in the 19th century. We have discussed his work before, in this blog, in the context of catena-commentaries. The connection between the two is perhaps something that should be explored.