@Incollection{elm1995irdische,
  author = {Elm, Kaspar},
  title  = {Die irdische und die himmlische, die verworfene und die heilige Stadt},

  year   = {1995},
  number = {},
  url    = {},

  const  = {\ text}
}
@Incollection{khnel1987earthly,
  author = {Kühnel, Bianca},
  title  = {From the Earthly to the Heavenly Jerusalem. Representation of the Holy City in Christian Art of the First Millennium},

  year   = {1987},
  number = {},
  url    = {},

  const  = {\ text}
}