In a journal, what's the difference between an "article" and a "monograph"?
The word monograph is derived from "mono" and "grapho", so the implied literal meaning is "writing on a single subject". Monographic sections are thus sections linked by a single theme, and often only have invited contributions. In the specific journal issue, the theme appears to be related to monuments/architecture from the Almohad Caliphate.

A journal that is clearer about what they mean with monographic sections is 
Kriterion Journal of Philosophy:


  Monographic sections are small collections of original research papers on a specific topic, with an introductory part, that are, in contradistinction to special issues, published as part of a regular issue together with other articles.