I've read a bit about how chapter/verse are/were decided in the Bible, different proposed versions, etc., but I can't seem to find out when/why this trend of two columns on a page started.
Was the goal simply to make the text more easily readable and navigable? Or is there some significance? And do we have any idea when this may have started?
According to the Bible publisher Crossway (publishers of the English Standard Version), the reasons are threefold:
Printing in a single column increases the page count by 10 to 25%, which increases how expensive it it to produce.
For the typical font size, the two columns increases readability (9-12 words per line is considered optimal)
Traditionally, the first printed Bibles were printed with two columns, as were ancient manuscripts handwritten by medieval monks.
However, there are some Bible editions written in a single column on the page. I have used several of them, it just depends on how the publisher is sizing the font and how thick they want to make it, and how big the book will be.
While I'd prefer to wait for a much more qualified person than I am to chime in, I believe it all started with the first Gutenberg Bibles, which had indeed forty-two lines of text over two columns; these, in turn, reflected the way prayer books were written before the adoption of the printing press.
Sources:
Well... this is going to be a bit awkward, as I'm currently helping out as an apprentice book-binder; but both Pio Colombo's and Piero Trevisani's Storia della Stampa ^1 - as well as my employer - agree with the theory. :-)
^1 in Enciclopedia Poligrafica, vol. I (Editrice Raggio, Roma 1953).
When the text was translated the two or multiple columns model was an ideal for having the original text side by side with a translation.
In 235 CE, Origen (a Christian scholar in Alexandria) completed the Hexapla, a comprehensive comparison of the ancient versions and Hebrew text side by side in six columns. In the first column was the Hebrew, in the second column was a Greek transliteration of it, then the newer Greek versions each in their own columns.
The translation of the Septuagint (Greek version of the Bible), by Sir Brenton, published in 1851, based primarily upon the Codex Vaticanus, (the Codex Vaticanus is itself one of the oldest extant manuscripts of the Greek Bible (Old and New Testament) and was written in three columns per page, with 40–44 lines per page, and 16–18 letters per line,) Brenton's model contains the Greek and English texts in two parallel columns.
Hence, the two columns model was extremely useful in preserving the original text side by side with the translated text and was done for the most part for the sake of translations, the tradition continued.
He Palaia Diatheke kata tous Ebdomekonta: the Greek Septuagint Version of the Old Testament according to the Vatican edition, together with the real Septuagint version of Daniel and the Apocrypha including the fourth book of Maccabees and an historical introduction. London: Samuel Bagster and Sons, 1851.