Physicians of Myddfai

Instructions for preparing herbal medicine attributed to the family have survived in the Red Book of Hergest, which dates from the late 14th century, and in other, more recent, Welsh manuscripts.

Rhiwallon, who supposedly lived in the parish of Myddfai in Carmarthenshire in the 12th century, and his sons Cadwgan, Gruffudd and Einion, were physicians whose skill became proverbial in medieval Wales.

[3] In the folk tale as set down by Rees,[4] a young man, son of a widow from Blaen Sawdde (near Llanddeusant) agreed to marry a beautiful girl who arose from the lake of Llyn y Fan Fach, with a promise that he would not hit her three times without cause, or she would return to her father.

He complied easily because the girl was so beautiful, and they were happy for years putting up a house in Esgair Llaethdy near Myddfai, and bringing up a family there.

One day she appeared to the eldest son, Rhiwallon, presented him with a collection of medicinal prescriptions and instructions, and told him that his future and that of his descendants was to be a healer.

A second manuscript of herbal remedies attributed to Rhiwallon's family, which was brought to light in the early 19th century, was said to have been copied from one in the possession of John Jones.

There was a revival of interest in herbalism in 18th-century Wales and a number of people had made further copies, including the scholar, Edward Lhuyd, Thomas Beynon of Greenmeadow and the bard and translator James Davies (Iago ab Dewi) of Llanllawddog.