The Law of Hywel Dda is the name given by the Welsh to the native law of Wales as it developed before the Edwardian conquest in 1283. The Law is preserved in a collection of manuscripts written between the early 13th and early 16th centuries, but containing much older material, the core of which is said to have been in some way the work of the mid-10th century king called Hywel Dda (H. the Good).
All very interesting, you say with a yawn, but why should I care about a bunch of medieval lawbooks from a thousand or more years ago?
If your intention is to understand the medieval Welsh, and the British tribes and kingdoms from whom they evolved, you should care a great deal. Do you want to know what was important to the early Welsh, what they valued and did not value, and more especially the valuation they placed on differing items and ideas? How a king's court was structured, and manned, and sustained? How the tribes and kindreds interacted, how property was inherited, how crimes were defined, and how compensated? All of this and more is in the Law of Hywel. True, it is a rag-bag collection, copied and recopied by lawyers who added and subtracted elements down the centuries according to what they deemed important, so that 9th and 13th century material mixes indiscriminately; while the researcher interested in earlier periods must guess and backdate, borrowing from other sources as she goes. But it is the best thing we have.
Some of it, moreover, is amusing reading. Among the King's officials is the Serjeant. "It is right for him to stand between the two posts and to watch lest the house should burn while the King is eating, and it is right for him to drink with the officials" -- two contradictory duties, one would think! The Porter, or gate-keeper, the laws say, "is entitled to a handful of every gift that comes through the gate ... berries and eggs and haddock. From every load of firewood that comes through the gate he is entitled to a stick which he can draw out without holding up the horse." The Falconer, among other things, is entitled to "a handsbreadth of wax candle from the Steward so as to feed his birds and make his bed." Furthermore, "on the day that he takes a notable bird" by his falcons "when the King is not at the place, when the falconer brings the bird to the court it is right for the King to rise before him; and if he does not rise ... to give the raiment he is wearing to the falconer." If a falcon belongs to a King, it is worth a pound, but if belongs to a villein, "whether it be a sparrowhawk or a falcon or any bird in the world ... it is of the same value as a hen: it is worth a penny." For of course a King's possessions are more valuable than those of a villein, whatever their quality.
But that's another post.
(Quotations in this article are from The Law of Hywel Dda: Law Texts from Medieval Wales translated and edited by Dafydd Jenkins: Gomer Press, 1990.)