Owen had engaged in a dispute about the boundaries of his lord ship of Olendwrdwy with Reginald lord Grey de Ruthyn, an Auglo Norman whose seignories adjoined his own. Taking advantage of the deposition of Richard, Lord Grey had forcibly possessed himself of a piece of land named Crocseu, which Owen, in the former reign, had recovered from him by course of law. Glendwr laid his case before parliament, but his suit was dismissed. To this provocation Reginald de Ruthyn added another insult, by purposely detaining the writ that had been issued to summon Owen, with the other barons, to assist Henry IV. in his expedition against the Scots. Lord Grey inisrepre seated to the king the absence of Gland we as an act of wilful disobe dience, and afterwards treacherously took possession of his lands, uuder the pretence of forfeiture. More temperate proceedings were advised by Trevor, bishop of St. Asaph; but uu representations of Owen's power had any iufluence on Lord Grey. The Welsh were at this time little better than barbarians : they hated the English because of the laws which punished their bards as vagabonds, allowed uo Welsh man to hold the smallest publio office iu his native country, and maintained foreign garrisons in their towns and castles. They were regarded in returu as an ungovernable, plundering, rebellious race. Out of their condition arose the power of Gleudwr. With the assist ance of the bards, who assertei him to be gifted with supernatural skill, his fame was spread through the whole of Wales, and his influence so rapidly increased, that, after levying a body of troops, ho at once proclaimed his genealogy, and laid claim to the throne of Wales. In the summer of 1400 he attacked the estates of his enemy Lord Grey, and in his absence seized upon his lands. As soon as the news of these exploits had reached the king, he sent lords Talbot and Grey to reduce Glendwr. Their attack upou his house was sudden, and he with difficulty escaped. lie next marched upon the town of Ituthyn, which he took, pillaged, and burnt during the time of a fair, and then retired to his fortifications in the hills. His pro ceedings were so alarming that the king soon resolved to march agaiust him in person. In September l4O0, a proclamation was issued from Northampton, commanding the lieutenants of Warwickshire, Leicestershire, and eight other counties to assemble forces, and on a given day to join the regular army at Coventry.
A grant was also made to the king's brother, John, earl of Somerset, of all Glendwr's estates in North and South Wales, in the hope that this powerful nobleman might be urged by the motive of immediate personal interest to dispossess the rebel of his property. Glencher's revenue in money did not exceed 300 marks (2000, but his rents in service and in kind were probably considerable. Notwithstanding all difficulties, his ranks were continually increased by fresh recruits. The king, who had now (1400) penetrated as far as the Isle of Anglcsea, plundered a Franciscan convent at Llanfaes, clew some and carried away others of the monks (who were however eventually restored to liberty), and repeoplcd the monastery with Euglish. The Franciscans were known to have assisted Prince Llewelyn, and to have espoused the cause of his successor. Henry at last caused his army to retire,
for the further prosecution of his expedition had been rendered useless by the retreat of Glendwr and hie troop) to the mouutains in the neighbourhood of Soowdon. At the suggestion of Niece Henry, a free pardon was offered to the rebels in several Welsh counties, which brought over to the king's authority thirty-two of the principal adherents of Glendwr. Nothing daunted by the diminution of his forces, but trusting as usual to the protection afforded by a moult tainoua country, Glendwr marched to Plinlimmon in the summer of 1401, and proceeded to ravage the surrounding country : he sacked Montgomery, burned the suburbs of Welshpool, destroyed Abbey ewm-Hir, and took the castle of Radnor, where he beheaded the garrison to the number of sixty. The Flemings (who in the reign of Henry L had settled in Pembrokeshire), incensed at his incursions, raised a force of 1500 men, and were so expeditious in their move ments, as, unexpected and unnoticed, to surround him at Mynydd Hyddgant. Hemmed in on every side, Glendwr broke through their ranks, and 200 of the Flemings remained dead upon the field. These depredations and victories awakened the fears of the king, and a second expedition into Wales was determined upon. Early in June (1401) the king was at the bead of his troops, but after razing to the ground the abbey of Ystrad FflOr, and pillaging the county of Cardigan, be withdrew his army, already exhausted by famine and disease. The extent of the popularity of Glendwr's cause among the Welsh may be estimated by a complaint now made by the Commons to the king and the upper house of parliament, that the Welsh scholars had left the English universities in order to aid in the rebellion at home, and that even the Welsh labourers had provided themselves with warlike weapons and quitted the service of their employers. In 1402 the event of a cornet was interpreted by the bards as an omen most favourable to his cause. Predictions gave new energy to his followers, acid Glendwr advanced towards Ruthyn, drew Lord Grey into the field, surprised him with an ambush, and carried him off captive to his camp near Snowdon : the prisoner's release was granted only upon the payment of 10,000 marks (66661.), and on his entering into an engagement to observe a strict neutrality. For his better security, or perhaps by compulsion, Lord Grey married Jane, the fourth daughter of Glendwr, immediately upon his liberation. Being now free from English opponents, he turned his arms against such of his conntrynaen as had adhered to the English or forsaken his cause : he marched upon Caernarvon, and closely blockaded the castle.
The cathedral of Bangor, and the cathedral, palace, and canons' houses at St. Asaph, were destroyed at Owen's command. His excuse for these outrages was that Trevor, bishop of St. Asaph, had been disloyal to Richard, from whom he had received his preferment. Trevor subsequently revolted from King Henry, allied himself to Glendwr, and did not quit the see, in which Owen confirmed him, until that chieftain's fortunes declined, when he prudently retreated to Paris.