Book of Deuteronomy have given various answers to the problem. The Deuteronomistic history theory is currently the most popular (Deuteronomy was originally just the law code and covenant, written to cement the religious reforms of Josiah, and later expanded to stand as the introduction to the full history); but there is an older theory which sees Deuteronomy as belonging to Numbers, and Joshua as a sort of supplement to it. This idea still has supporters, but the mainstream understanding is that Deuteronomy, after becoming the introduction to the history, was later detached from it and included with Genesis-Exodus-Leviticus-Numbers because it already had Moses
Development of the Old Testament canon phrase "Old Testament", which is associated with Supersessionism. The first list of Old Testament books compiled by a Christian source is recorded by the 4th century historian Eusebius. Eusebius describes the collection of a 2nd century bishop, Melito of Sardis. Melito's list, dated to circa 170, the result of a trip to the Holy Land (probably the famous library at Caesarea Maritima) to determine both the order and number of books in the Hebrew Bible, instead seems to follow the order of the books presented in the Septuagint. Melito's list, as cited by Eusebius, as follows: According to Archibald Alexander,