Seven tribes are asking an Alabama university to return the remains of nearly 6,000 people excavated over the years from what once was one of the largest Native American settlements in North America.

The Oklahoma-based Muscogee Nation, Choctaw Nation of Oklahoma and five other tribes have filed a petition under a federal law for the return of 5,982 "human remains of our ancestors" and funerary objects now held by the University of Alabama and its Moundville Archaeological Park.

"These are human beings. We consider them to be our grandparents," Raelynn Butler, the Muscogee Nation's historic and...