Approximately ten years after Lehi and his family left Jerusalem (ca. 590 B.C.), Nephi was commanded to begin a record of his proceedings, the record we have come to know as the large plates. On this set of plates he was to record such matters as the nature of the family’s travels, the genealogy of his father, many of the prophecies of Lehi, the wars and struggles of his people, and the details of the reigns of the kings. (See 1 Nephi 9; 1 Nephi 19:1-6.)
About twenty years later (ca. 570 B.C.) Nephi was given an additional writing assignment: he was Lo begin a record which would concentrate upon spiritual matters, the dealings and revelations of God with the Lehites. (2 Nephi 5:29-33.) This record, known to us as the small plates, covers the material in the Book of Mormon from 1 Nephi through the book of Omni (143 pages in the 1981 edition), approximately 475 years of Nephite history. At the time of King Benjamin (Mosiah 1), the small plates came to a close, and the large plates were thereafter used to record both secular and spiritual doings.