Möckern was originally called "Mokrianici" by the Slavs who settled in the area in the 7th and 8th centuries. The name meant "a humid place," a reference to the formation, at that time, of extensive marshes around the Ehle River. By the middle of the 10th century, the settlement was an established German burgward, but it is believed that by the end of the 9th century, the settlement was already under German influence. As such, the burgward was obliged by a document from Otto I the Great in 948 to pay a tithe to the Magdeburg Moritz monastery. This document is considered to be the first mention of the place. At this period, a fortress was built on the site of the old Slavic settlement, and its keep is still part of the fortress today. The castle served as an outpost to protect Magdeburg and secured the important roads to Brandenburg and Zerbst. In 955, Otto I is supposed to have founded Möckern's parish church, following his victory over Hungary on August 10 of that year. Because that day is (St. Lawrence Day), the church was named for the saint. In the 11th century, Möckern acquired a defensive wall (made of boulders since the 12th century), which was equipped with three gates. Möckern already had its town charter.