Chapter and verse
While running titles
told the reader what text was found on a particular page, the chapter number narrowed down its contents even further. As with many other navigational aids, the practice of numbering the chapters goes back to the Carolingian Age. They appear to have become standardized much later, however, perhaps as late as the twelfth century.
In the thirteenth century, a Bible redaction was made in Paris (the "Paris Bible") wherein the numbering of the chapters became standardized, something that was not a given before then. This meant that two individuals discussing Genesis 15 were actually talking about the same text for the first time. Many works used in university education had an additional tool to define the location within the text even more precisely, the paragraph