Eusebian Canons

[5] The canon tables were made to create a sense of divinity within the reader’s soul, to understand and reflect upon the various colors and patterns to achieve a higher connection with God.

It was traditionally believed that he divided the four Gospels into small numbered sections, which were similar in content where the narratives are parallel.

It is now believed that the work of Ammonius was restricted to what Eusebius of Caesarea (265-340) states concerning it in his letter to Carpianus, namely, that he placed the parallel passages of the last three Gospels alongside the text of Matthew, and the sections traditionally credited to Ammonius are now ascribed to Eusebius, who was always credited with the final form of the tables.

[7] The harmony of Ammonius suggested to Eusebius, as he says in his letter, the idea of drawing up ten tables (kanones) in which the sections in question were so classified as to show at a glance where each Gospel agreed with or differed from the others.

The tables themselves were usually placed at the start of a Gospel Book; in illuminated works they were placed in round-headed arcade-like frames, of which the general form remained remarkably consistent through to the Romanesque period.

Canon tables from the Garima Gospels , Ethiopic gospel manuscripts of the sixth century; showing original Late Antique arcaded forms subsequently perpetuated in Byzantine and Romanesque manuscripts
Canon table from the Book of Kells ; the tables in the book were effectively unusable, as they were over-condensed and the corresponding sections were not marked in the main text. This is either because it is unfinished, or because it was a display book not meant for study.
An Armenian illuminated manuscript of a canon table by Toros Roslin (active 1256 - 1268) entitled Canon Table Page.
Canon quartus in quo III from the Cutbercht Gospels (8th century, Salzburg)