Abbot Erpo's abbatate, the first heyday of Kloosterrade

After the death of Abbot Richer in 1122 a period of internal tension and unrest began at the administrative level in Kloosterrade. Due to disagreements, the canons failed to elect a leader from their own circle. The cause was probably the lack of strong personalities suitable for the position of abbot, or else the eagerness with which one or two posed as the new leader was seen as a threat to togetherness. On up to four occasions clergymen from outside the abbey were elected superior. However, all these elections were always controversial and proved time and again to be a disappointment. Conflicts that arose as a result of disagreements over the interpretation of the monastic rule or attempts to adapt the monastic customs to stricter rules led to superiors being removed from office by the bishop or pope or superiors choosing to leave the abbey themselves. In 1134 Borno was elected superior for the second time. He had been elected ten years earlier and then wanted to expand choir prayer. This attempt met with fierce opposition, and none other than the pope ruled that the old customs should be maintained. That left Borno with no choice but to leave Kloosterrade. With his return the internal contradictions ebbed away. Significant and of great importance for the inner consolidation of the monastic community was the decision taken by the choirmasters in 1137 after Borno's death. From now on they would elect only superiors from their own community, preferably fellow brothers who had been taught in the abbey school and raised in monastic discipline from their youth.

With the Maastricht-born Erpo, Kloosterrade got superior in 1141 who had been formed in the abbey from childhood. His long abbacy lasted at least until 1178 and acted as a stabilising factor. Not without reason, this period is hailed in historiography as the golden age of medieval Kloosterrade. For decades, economic prosperity, piety, scholarship and spirituality prevailed. Now the Consuetudines, the precepts and customs introduced from Rottenbuch by Abbot Richer and subsequently modelled on the example of the monastery of Springiersbach, were given their final form, concluding the development into a convent with a moderate ordo novus as its precept. In some respects Erpo left his mark on a stricter observance of the monastic rule. By abolishing the use of fat in all food, he carried through the austerity of eating habits for which Abbot Richer, who forbade the consumption of meat, had set the tone. In addition, he introduced the silentium, a time of silence, by which he imposed a literal prohibition on the choristers from speaking outside the service times of choral prayer. On the other hand, Erpo believed that the celebration of the tides "per diem et noctem," in which the services of choral prayer lasted almost continuously from midnight to midnight, required too much of the canons. In addition to the aggravations of the rule of life he imposed, he therefore simplified the overloaded liturgical programme. He limited daily choral prayers to the tides proper and eliminated extras such as praying the separate Maria Office and singing the fifteen psalms before the metre and the seven penitential psalms before the priem. With these adjustments to the observance of the precepts and the arrangement of choral prayer, the development of Kloosterrade under Abbot Erpo reached its completion. Thus, after only half a century, the abbey reached its climax: Kloosterrade was the first community between the Rhine and the Scheldt to live according to the new guideline of the Rule of St. Augustine and, because of the uniqueness of its Consuetudines, it enjoyed supra-regional prestige. For other Augustinian monasteries pursuing reform, Kloosterrade served as an example.

Characteristic of Kloosterrade Abbey in the twelfth and in the first half of the thirteenth centuries was its status as a double monastery. From the entry of ministerial Embrico together with his wife Adeleida and their children Heriman and Margareta, a community of nuns had been established in addition to the male convent. This development was not in accordance with the views of the founder Ailbertus. In 1140 superior Johan managed to find accommodation for the nuns outside the walls of Kloosterrade. However, Abbot Erpo again admitted women, because he found a conclusive motive for his decision in the need for nuns to perform a variety of domestic tasks. Over the next few decades, however, the influx of monks was much greater than expected, and the problem of an undesirable mixed society arose again. The status of double monastery would come to an end only in 1243, with the transfer of the nuns to the monastery in Sinnich that had newly been founded by Abbot Marsilius .

The performance of pastoral care was equally undesirable and inconsistent with the ideal of an ascetic and contemplative monastic life that had been the abbey's initial aspiration. Abbot Erpo's predecessor, Superior Johan, abandoned this stance in 1140 when he made the decision to exercise parochial pastoral care and accepted the ministry of the church in Kerkrade by choristers of the abbey. Toward the end of Erpo's abbacy, Kloosterrade acquired the patronage rights of several parish churches. In this way, the abbey's sphere of influence assumed wide proportions between Meuse and Rhine.

A tangible reminder of the abbey's heyday is the monastic chronicle created around 1160 during Erpo's abbatial period. The medieval manuscript, which has no title or inscription, was written by three unknown chroniclers and belongs to the genre of "narrationes fundationis". In it, the story of the foundation of a monastery, the life of its founder and mostly its further history are told. Such chronicles were written with great care and attention in the scriptorium of the abbey or monastery, often by anonymous monks of the second generation. The Annales Rodenses tell the life story of Ailbertus, his education and schooling in Tournai, and his search for the place where he could live as a hermit. Then the chronicle recounts the history of the first five decades of the abbey, from the arrival of Ailbertus in 1104 to the last entry from the year 1157. The manuscript owes its name Annales Rodenses, by which it has remained known,  to choirmaster Nicolaas Heyendal, who wrote a continuation of the history of Kloosterrade toward the end of the seventeenth century. The importance of the chronicle of Kloosterrade for historiography is shown by the fact that data from the period after 1157 are very scarce. Other sources from which can be drawn to trace the ins and outs and fortunes of the abbey in the late Middle Ages are limited to only a few surviving charters.

Abbot Erpo also knew how to give Kloosterrade prestige in material terms. No fewer than 16 charters from the period 1141 to 1177 testify to this, in which donations and purchases of land and the acquisition of rights to revenues are sealed. By the end of Erpo's tenure, presumably in 1178, the domain of the abbey had reached a size of 3,570 hectares. Although almost half of this was due to donations or had been made by entering mons and nuns, over one-fifth of the land holdings were purchased by Abbot Erpo. Such an increase is indicative of the prosperity the abbey enjoyed in those days. After 1178 the increase in land holdings stagnated. The income that the abbey acquired thereafter consisted mainly of rents and property tax. In the period of decline after the War of Limburg Succession and in later times, especially in the sixteenth century, the abbey had to sell a considerable part of its property out of financial necessity and to finance repair costs of damage to church and monastery buildings incurred during wars and looting.

It is not known when Abbot Erpo died. His successor, abbot Rutger, is first mentioned as abbot of Kloosterrade in 1186. He then acts as a witness to the donation by Duke Hendrik III of Limburg to the abbey of Floreffe as shown by the charter confirming this donation.