MLA

Wolfram, von Eschenbach, active 12th century. Willehalm. [between 1300 and 1315]. https://collections.library.yale.edu/catalog/2056679.

APA, 6th edition

Wolfram, von Eschenbach, active 12th century. ([between 1300 and 1315])[Willehalm]. https://collections.library.yale.edu/catalog/2056679.