2 Kings 22 reports that during repairs to the temple in the reign of Josiah, the high priest found a book of the law. It was read to the king, who tore his clothes, and a reform followed: the local shrines were destroyed, the countryside priesthood was brought to Jerusalem, and a Passover was kept of a kind the text says had not been kept since the days of the judges.
Deuteronomy is the only book in the Torah that demands precisely that programme. The centralisation of sacrifice at one chosen place, the abolition of the high places, the provision for displaced Levites, the particular form of Passover, all of it is in chapters 12 to 26 and in none of the other four books.
At the beginning of the nineteenth century, W. M. L. de Wette proposed in his doctoral dissertation that the scroll found in the temple was Deuteronomy, or a core of it. The proposal was small and its consequences were not. It supplied the first fixed date anywhere in the Pentateuch, and every later reconstruction of how the Torah was assembled was calibrated against it, dating the other sources as earlier or later than that one anchor.
What is still argued is what actually happened in the temple. The narrative may report a genuine discovery of an older text. The book may have been composed, or substantially rewritten, by the party pressing for the reform and produced at the moment it would carry most weight. A third reading treats the account itself as later, written to give the reform an authority it did not have at the time. The evidence does not decide between them, and the atlas does not either.