The 'Laws of Hywel Dda' is the term applied to a system of native Welsh law named after Hywel Dda (died 950). He is credited with its codification. None of the surviving Welsh law manuscripts, however, are earlier than the second quarter of the 13th century. Although they contain a law that is of 12th and 13th century origin, scholars are agreed that these manuscripts contain a core of matter that is much earlier in date. Most of these books are small in size as is NLW MS 20143A (166 x 131 mm.). They were probably designed as 'pocket-books' to be carried about by lawyers rather than to be kept on library shelves.