"The Physicians of Myddfai"("Meddygon Myddvai" in Welsh), or "The medical practice of the celebrated Rhiwallon and his sons, of Myddfai, in Carmarthenshire, physicians to Rhys Gryg, lord of Dynevor and Ystrad Towy", was written about the middle of the 13th century. The collection of herbal remedies are associated with Rhiwallon Feddyg (eldest son of the Lady of the Lake), founder of a medical dynasty that lasted over 500 years and comes from the manuscript called the "Red Book of Hergest", a large vellum manuscript written in Welsh shortly after 1382. The manuscript derives its name from the colour of its leather binding and from its association with Hergest Court between the late 15th and early 17th century. The Physicians of Myddfai practised in the village of Myddfai near the market town of Llandovery in Wales, healing subjects with their herb lore and potions as well as their mystical powers and insight into the human condition.