The ancient Romans seem to have been the first to consider the divisions of a text as small heads contributing to the body of the whole. Our word ‘chapter’ comes from the Latin capitulum, the diminutive of caput for head. The chapters are small heads, from which the corpus or body of the text emerges.
Whereever you look on the page, there are heads. The ‘header’ is one, and so are the chapters. If you can’t make heads or tails of a book, now you know why.
The word capitulum also described the capital of a column, the head on top of the pillar. The anthropomorphic approach to books and architecture in antiquity echoed the larger ideas about the universe, a living and breathing organism with the human micro-organism at its centre. Not because human beings were full of themselves then (for nothing really changed in human presumption in the passage from geo to helio-centrism), but because the ancients figured out the riddle of the universe: nothing makes sense unless it makes sense to the one making sense of it all. And the human perspective is the only real perspective we have, despite claims to the contrary.