The D scholia, or scholia Didymi, named erroneously for Didymus, are the earliest and largest group. They occur primarily in the 9th century Z (Rome, Biblioteca Nazionale), and the 11th century Q, but also in some others, such as A and T. The D scholia were once thought to be the work of the 1st century BCE scholar Didymus; they are now known to go back to 5th and 4th century BC school manuscripts, pre-dating the Alexandrine tradition, and representing “the oldest surviving stratum of Homeric scholarship.” Some are also called the scholia minora and the scholia vulgata, the former name referring to the short length of many. These are glossaries. Among the non-minor scholia are mythological (allegorical) aetia, plots, and paraphrases, explaining the meanings of obscure words.