The rising of the earls was only the first and the least dangerous of the trials of Henry IV. Only a few months after their death a rebellion of a far more formidable sort broke out in Wales--where Richard II. had been popular, and the house of March, his natural heirs, held large estates. The leader was a gentleman named Owen Glendower, who had the blood of the ancient kings of Gwynedd in his veins. Originally he had taken to the hills as a mere outlaw, in consequence of a quarrel with one of the marcher barons; but after many small successes he began to be recognized as a national leader by his countrymen, and proclaimed himself prince of Wales. The king marched against him in person in 1400 and 1401, but Glendower showed himself a master of guerrilla warfare; he refused battle, and defied pursuit in his mountains, till the stores of the English army were exhausted and Henry was forced to retire. His prestige as a general was shaken, and his treasury exhausted by these fruitless irregular campaigns. Discontent of the commons. Statute De heretico comburendo. Meanwhile worse troubles were to come. The commons were beginning to murmur at the king's administration; they had obtained neither the peace nor the diminished taxation which they had been promised. Moreover, among some classes at least, he had won desperate hatred by his policy in matters of religion. One of his chief supporters in 1399 had been Archbishop Arundel, an old enemy of Richard II. and brother to the earl who had been beheaded in 1397. Arundel was determined to extirpate the Lollards, and used his influence on the king to induce him to frame and pass through parliament the detestable statute _De heretico comburendo_, which recognized death by burning at the stake as the penalty of heresy, and bound the civil authorities to arrest, hand over to the church courts, and receive back for execution, all contumacious Lollards. Henry himself does not seem to have been particularly enthusiastic for persecution, but in order to keep the church party on his side he was forced to sanction it. The burnings began with that of William Sawtré, a London vicar, on the 2nd of March 1401; they continued intermittently throughout the reign. The victims were nearly all clergy or citizens; the king shrank from touching the Lollards of higher rank, and even employed in his service some who were notoriously tainted with heresy. War with Scotland. Battle of Homildon Hill. Conspiracy of Northumberland with Glendower.