The Diocese of Eger was plundered and devastated by the invading Mongols in 1241–42. Lampert committed to reclaiming the lost estates and property of the diocese. Under his reign, the destroyed Eger Cathedral was renovated and rebuilt. King Béla IV of Hungary sought to strengthen the bishopric with land donations. He placed the relatively newly formed Sáros County under the jurisdiction of the Diocese of Eger in 1248. In the same year, the king returned the village of Cserép to the bishopric, which was unlawfully seized by Ernye Ákos. Lampert was also granted three villages with port duties along the river Tisza, including Csege and Örvény (present-day a borough in Tiszafüred), in addition to the Ohat Abbey in the western part of Hortobágy. Lampert was permitted to build a stone castle in Füzérkő (also known as Kerekkő), near present-day Bükkzsérc, which laid in the Bükk Mountains. The castle was erected in the following years, but it did not play a significant role in the future and presumably was demolished by the early 14th century.