The order of an early edition of the letters of Paul is based on the size of the letters: longest to shortest, though keeping 1 and 2 Corinthians and 1 and 2 Thessalonians together. The Pastoral epistles were apparently not part of the "Corpus Paulinum" in which this order originated and were later inserted after 2 Thessalonians and before Philemon. Hebrews was variously incorporated into the "Corpus Paulinum" either after 2 Thessalonians, after Philemon (i.e. at the very end), or after Romans.