Vaticanus, Codex—is said to be the oldest extant vellum manuscript. It and the Codex Sinaiticus are the two oldest uncial manuscripts. They were probably written in the fourth century. The Vaticanus was placed in the Vatican Library at Rome by Pope Nicolas V. in 1448, its previous history being unknown. It originally consisted in all probability of a complete copy of the Septuagint and of the New Testament. It is now imperfect, and consists of 759 thin, delicate leaves, of which the New Testament fills 142. Like the Sinaiticus, it is of the greatest value to Biblical scholars in aiding in the formation of a correct text of the New Testament. It is referred to by critics as Codex B.