It is widely recognized that the ending of Mark in the Codex Sinaiticus, Vaticanus and Alexandrinus presents some physical peculiarities in terms of the layout, quire structure and handwriting. This paper reconsiders these peculiarities from a codicological perspective. The main focus is on the physical arrangement of the ending of Mark in the three above-mentioned biblical pandects. It attempts to reconstruct the content organization of the replaced bifolio in the Sinaiticus, the original quire organization at the end of Mark in the Alexandrinus (including a forgotten blank folio) and offers a new solution for the empty columns at the end of the Vaticanus. It evaluates the plausibility of the explanations proposed by previous scholarship on this subject.Secondly, it places these three situations within the wider perspective of the irregularities which can be observed in the transition between gospels and at the end of gospel series in pre-ninth-century manuscripts and attempts to determine if there are recurring features in the ending of Mark which could explain some of the peculiarities observed in the three pandects. The conclusion sets out some of the work which remains to be done in order to better understand the physical characteristics of the ending of Mark in ancient manuscripts.