The term "Holstein" derives from Old Saxon "Holseta Land," ("Holz" and "Holt" mean wood in modern Standardised German and in literary English, respectively). Originally, it referred to the central of the three Saxon tribes north of the River Elbe: "Tedmarsgoi" (Dithmarschen), Holstein and "Sturmarii" (Stormarn). The area of the tribe of the Holsts was between the Stör River and Hamburg, and after Christianization, their main church was in Schenefeld. Saxon Holstein became a part of the Holy Roman Empire after Charlemagne's Saxon campaigns in the late eighth century. Since 811, the northern frontier of Holstein (and thus the Empire) was marked by the River Eider.