@book { GrenzenundStadttorevonBerlin,
    title = "Grenzen und Stadttore von Berlin",
    author = "Stefan {Hirtz}",
    year = "2000",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832424435",
    url = "https://m.diplom.de/document/218241"
}