18 February 1366: The Viceroy, Lionel Duke of Clarence and Earl of Ulster and son of the King of England, summoned a Parliament at Kilkenny on this day. From this emerged the series of infamous ordinances that became known as the ‘Statutes of Kilkenny’ and were designed to put a legal framework on the division of Ireland into two separate peoples: the English and the Irish. It contained thirty-five chapters of note.
For instance if any man took a name after the Irish fashion, used the Irish language, or dress, or mode of riding (without saddle), or adopted any other Irish customs, all his lands and houses were forfeited, and he himself was put into jail till he could find security that he would comply with the law. The Irish living among the English were permitted to remain, but were forbidden to use the Irish language under the same penalty. To use or submit to the Brehon law or to exact coyne and livery was treason.
Lionel's wife died in Dublin in 1363, leaving behind a daughter, Philippa, whose descendants would one day claim the throne for the House of York. A second marriage was arranged for Lionel with Violante, daughter of Visconti, lord of Pavia; the enormous dowry which Galeazzo promised with his daughter being exaggerated by the rumour of the time.
Journeying to fetch his bride, Lionel was received in great state both in France and Italy, and was married to Violante at Milan on 28 May 1368. Some months were then spent in festivities, during which Lionel was taken ill at Alba, where he died. There was strong speculation at the time that he had been poisoned by his father-in-law although this has never been proven.
The Statute of Kilkenny, though not exhibiting quite so hostile a spirit against the Irish as we find sometimes represented, yet carried out consistently the vicious and fatal policy of separation adopted by the government from the beginning. It was intended to apply only to the English, and was framed entirely in their interests. Its chief aim was to withdraw them from all contact with the "Irish enemies"--so the natives are designated all through the act--to separate the two races for evermore.
From A Concise History of Ireland by P. W. Joyce