@incollection{baumgartner2007reich,
  author = {Baumgärtner, Ingrid},
  title = {Das Reich der Staufer},
  booktitle = {Das Verdämmern der Macht. Vom Untergang großer Reiche},
  year = {2007},
  pages = {60-81},
  url = {http://nbn-resolving.org/urn/resolver.pl?urn=urn:nbn:de:hebis:34-2007020617092}
}

@article{rosenthal1973invention,
  author = {Rosenthal, Earl},
  title = {The Invention of the Columnar Device of Emperor Charles V at the Court of Burgundy in Flanders in 1516},
  journal = {Journal of the Warburg and Courtauld Institutes},
  year = {1973},
  volume = {36},
  pages = {198-230}
}

@article{rosenthal1971ultra,
  author = {Rosenthal, Earl},
  title = {Plus ultra, non plus ultra, and the Columnar Device of Emperor Charles V},
  journal = {Journal of the Warburg and Courtauld Institutes},
  year = {1971},
  volume = {34},
  pages = {204-228}
}