What is Phonological history of Spanish coronal fricatives?

In Spanish dialectology, the realization of coronal fricatives is one of the most prominent features distinguishing various dialect regions. The main three realizations are the phonemic distinction between /θ/ and /s/ , the presence of only alveolar , or, less commonly, the presence of only a denti-alveolar that is similar to /θ/.

While an urban legend attributes the presence of the dental fricative to a Spanish king with a lisp, the various realizations of these coronal fricatives are actually a result of historical processes that date to the 15th century.