Burckhardt 1999, p. 168: "The establishment of these Panhellenic sites, which yet remained exclusively Hellenic, was a very important element in the growth and self-consciousness of Hellenic nationalism; it was uniquely decisive in breaking down enmity between tribes, and remained the most powerful obstacle to fragmentation into mutually hostile poleis." Burckhardt, Jacob (1999) [1872]. The Greeks and Greek Civilization. New York: St. Martin's Press. ISBN978-0-312-24447-7.