This is the flag of the Benin Empire. From the Wikipedia:
The Benin Empire or Edo Empire (1440-1897) was a pre-colonial African state of modern Nigeria. It is not to be confused with the modern-day country called Benin (and formerly called Dahomey).
Don’t EVER confuse them with the modern-day country called Benin! EVER!!
Thanks to kottke.org for the find.
