Nibelungenlied

Nibelungenlied was a book written by an unknown author, obtained by Ezio Auditore da Firenze in the 16 th century in Constantinople.

Summary
''A tragic tale of lost love, revenge, and slain dragons, written sometime in the twelfth century, but based primarily on Germanic, pre-Christian sources. Nobody knows who wrote the "Nibelungenlied" but most scholars agree that he probably wore a long beard and walked with t glowing staff.''

Source

 * Assassin's Creed: Revelations