Generalities
Canon law was not a finished product from the beginning, but rather a gradual growth. This is especially true of the earlier Christian centuries. Such written laws as existed were not originally universal laws, but local or provincial statutes. Hence arose the necessity of collecting or codifying them. Earlier collections are brief and contain few laws that are chronologically certain. Only with the increase of legislation did a methodical classification become necessary.
These collections may be genuine (e. g. the Versio Hispanica), or apocryphal, i.e. made with the help of documents forged, interpolated, wrongly attributed or otherwise defective (e. g. the Pseudo-Isidore collection). They may be official and authentic (i.e. promulgated by competent authority) or private, the work of individuals. The forged collections of the middle of the ninth century are treated in the article on False Decretals.
Read more about this topic: Collections Of Ancient Canons