@book { DerWendenkreuzzugvon1147,
    title = "Der Wendenkreuzzug von 1147",
    author = "Jan-Christoph {Herrmann}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1107777"
}