This article deals with the issue of the collection and formation of the Corpus Paulinum. It argues that a collection of Pauline letters to seven churches was crucial to this development. This collection possibly also included Hebrews in conjunction with Romans, but not Philemon. Another parallel collection was made of four letters to individuals, but was not popularised until later. When the two collections were merged into the present Corpus Paulinum, their respective order based on decreasing length was preserved, and they were placed alongside each other. As for Hebrews, it was relegated to the end due to the controversy regarding its authorship.