Assembly:

After the finalization of the parchment leaves those making the manuscript would move to the binding of the codex.  By this point, the leaves were already collected into loosely bound quires, though frequently disordered.  In order to order the pages the man assembling the codex would add -- or rely on the transcribing scribe to add -- numbers "in the lower margin of the first or last page of each quire."  These "quire numerals" consisted of a Roman numeral, "sometimes surrounded by some form of decoration, and sometimes preceded by the letter Q, abbreviating Quaternio or Quinio" (Graham and Clemens 49).  While many of these quire numerals have been lost to trimming of the manuscript leaves, they are sometimes still visible along the bottom margin of the page. 

In lieu of quire numerals, scribes sometimes relied on catchwords to aid in the assembly and ordering of pages.  Also called stitchwords, these were "the word or words with which the first page of the next quire began" and were written "in the lower margin of the last page of [the preceding] quire" (Graham and Clemens 49).  At the time of assembly, the binder could verify the catchwords to ensure that they matched the words beginning the next quires.  These catchwords were generally written horizontally in the lower margin, but in the fifteenth century, "catchwords were often written vertically" and occasionally provided with a decorative frame (Graham and Clemens 49).

To the left is an example of a catchword surrounded by a decorative griffin in the lower left margin of the text; to the right, a manuscript leaf with a quire signature (IIII) in the lower margin.