Roger Pearse writes,
Not everyone will know what a “catena” (the word means “chain”) is. The term itself is modern. It refers to medieval Greek biblical commentaries. These are composed entirely of extracts from earlier writers, chained together by slight wording alterations at the ends. They usually appear in the margins of Greek bibles; or, rather, the biblical text appears in a small box in the centre of the page, surrounded by a mass of small writing! The author of each catena entry is indicated, usually using the first letter of their name or something of the kind. This of course gives plenty of scope for misattribution! Often the main author used is John Chrysostom.Read more,
Catenas seem to arise in the 6th century, and often incorporate very interesting material. There can be several catenas for each book of the bible, and the relationships between them are tangled things.
If you do you'll be able to work out what my interest in this is.