September 16th is the anniversary of the proclamation in 1400, of Owain Glyndwr as Prince of Wales and is now celebrated annually as Owain Glyndwr Day.
Owain Glyndŵr's uprising began with a dispute during 1399 and 1400 over a piece of land that Glyndwr claimed had been stolen by his neighbour, the Marcher Lord, Sir Reginald de Grey. When Glyndwr received no justice from King Henry IV and his repeated appeals were ignored, he felt that he was left with no option other than to rebel against the unjust and oppressive rule of the English.
Word of Glyndwr's stance struck a chord with other disaffected Welsh people and he became the symbolic leader of the resistance movement against the crown and the arrogant Marcher Lords. Glyndŵr raised his banner on the outskirts of Ruthin on 16th September 1400 and was proclaimed by his followers as Prince of Wales.
The men of Wales flocked in droves to Owain's banner as word of the revolt spread like wildfire throughout the country and many exiled Welsh people returned to join what had become a widespread national uprising. The first attack in 1400 was on Ruthin, followed by those on Rhuddlan, Flint, Holt, Oswestry and Welshpool. Glyndŵr held a Parliament at Machynlleth in 1404 and in 1406, wrote to King Charles VI of France, asking for his support in achieving Welsh independence, explaining his vision for establishing two Welsh universities and an independent Welsh Church.
However in 1409, Glyndwr had become besieged at Harlech Castle and this in effect was the end of the uprising. He did make his escape and remained unbetrayed and uncaptured until his supposed death in 1416.