After the complete subjugation of the Saxons, S. Ludger was directed by the emperor to repair into Westphalia. He erected a monastery where now stands the episcopal city of Münster, and travelled over the district with unflagging energy, wearing no hood, as his biographer says, with which monks usually keep their heads and shoulders warm, instructed the barbarous tribes, and appointed priests to minister the sacraments to them. He was soon after ordained bishop by Hildebold, archbishop of Cologne. His heart now turned to the wild Normans, the scourge of all the maritime peoples of Gaul and on the Baltic.
As bishop, he ministered to his Saxon flock with great judgment and gentleness, and that proud conquered people yielded more to his gentle persuasion than to the harsh commands of Charlemagne. He still ruled Friesland, which he had brought to the faith. Charlemagne also set him over a monastery in Brabant. Thus his dream of the three heaps, signifying his rule over three peoples, was fulfilled.
The chief seat of his diocese was in the canton Sudergau, at a place called Mimigardford (or, more properly, Miningardvard, the fort of Miningard) on the Aa, where he built a monastery by the river for the Regular Canons.
From this establishment the city eventually took its name of Münster, though the bishops continued to style themselves "of Mimigard" to the time of Thierry II.
He built the cathedral of S. Paul at Münster. The five Frisian counties contributed largely towards the cost. Their liberality was commemorated in a sculpture representing them offering gifts to S. Paul, which once stood near the N.W. door of the cathedral. It was defaced by the Anabaptists in 1535.
He uprooted idolatry, sowed the Word of God, built churches, and ordained priests to minister in them. He desired to bring many nations to the knowledge of the true God, and volunteered to preach to the heathen Northmen, but Charlemagne refused his consent.
The blameless conduct of Ludger did not save him from detractors, nay, perhaps it rather incited their malice. He was accused (as the anonymous Frieslander who wrote his life tells us) to Charlemagne of penuriousness in decorating the houses of God. The emperor summoned him to court, and on the morning after his arrival the chamberlain was sent to call him before the council. He found Ludger saying the divine office. Our saint promised to come as soon as it was done. A second and a third messenger summoned him, but he did not go to the emperor till the office was over. Charlemagne asked him, "Why didst thou disregard my command to come at once?" The saint said, "God is to be preferred to thee, O king, and to all men." The emperor, pleased at his reply, exclaimed, "I am thankful that I have found thee such as I ever esteemed thee, and I promise never again to give ear to those who calumniate thee." Once Ludger imposed a severe penance on a priest who left off saying the office that he might blow the fire, as they were saying Matins in their travelling tent, because the smoke was driving into the bishop's face; for the saint desired to teach his clergy that they ought to suffer nothing to disturb them when saying the Divine office.
Altfrid adds that S. Ludger "was well read in Holy Writ," as is clearly proved in the book he wrote about the life of Gregory and Albric; moreover, he wrote an account of the early events which took place at the coming of S. Boniface and at his ordination. His meaning, probably, is not that separate lives of these holy men were written by Ludger, but that notices of them were inserted in his "Life of Gregory." This is the only genuine work of his that has survived, for the epistle on the canonization of S. Suibert is not from his pen.
When he felt his end approaching, he devoted more time than before to reading Holy Writ, to chanting Psalms, and, though feeble in body, he celebrated Mass every day.
On the day of his death, March 26th, 809, very early, he heard Mass at Coesfeld, and preached; then hastening to Billerbeck, arrived there at nine o'clock the same morning, preached again, and celebrated his last Mass. That evening he gently expired.