A rare medieval manuscript, written in the ancient Welsh language, is set to highlight Sotheby's Western Manuscripts and Miniatures sale on July 10.

The sale will be the first time the manuscript has seen British soil for over 150 years, having originally been taken to America by Welsh settlers in the 1700s. Entitled The Laws of Hywel Dda, the manuscript has been attributed to King Howel the Good (c. 880-950), who sets out his surprisingly liberal rules over 99 vellum leaves.

Howel's laws are part derived from the ancient Celtic justice system and certainly explain how the king got his name. A forward-thinking ruler, he focused his laws on compensating the victims of crime, rather than violent punishments for the perpetrator. He is especially kind to women in the manuscript, who, under Howel the Good, were entitled to reimbursement should their husbands commit adultery.

But it is not for its progressive views that the manuscript is so highly valued by collectors; it provides an exceedingly rare insight into the medieval Welsh language. There are currently only 80 extant manuscripts written in the language, the majority of which are held in the British Library and the National Library of Wales.

In fact, medieval Welsh manuscripts are so rare that the last time one appeared at auction was in 1923. Sotheby's has valued the work at £500,000-700,000 ($781,000-1m), although Paul Fraser Collectibles expects it to exceed this estimate, given that it is likely the last to appear on the market.

The July 10 auction will also feature a brilliant sex guidance manuscript, which was written for Essex nuns circa 800 AD. 

We have our own superb selection of rare manuscripts here, highlighted by this King Henry VIII personal divorce plea. See our latest free newsletter for great advice on why now is the time to invest in English manuscripts.