Kirkpatrick Sale, After Eden: The evolution of human domination (Duke University Press, 2006), 48; Google Books.
Lance Grande, Gems and gemstones: Timeless natural beauty of the mineral world (Sicagi: University of Chicago Press, 2009), 292.ISBN 978-0-226-30511-0: "The oldest known gold jewelry in the world is from an archaeological site in Varna Necropolis, Bulgaria, and is over 6,000 years old (radiocarbon dated between 4,600BC and 4,200BC)."
culture.gouv.fr
Rectio Franciae, "The Gumelnita Culture": "The Necropolis at Varna is an important site in understanding this culture."
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revistapontica.files.wordpress.com
Vladimir Slavchev, "Monuments of the final phase of Cultures Hamangia and Savia on the territory of Bulgaria," Revista Pontica 37–38 (2004–2005): 9–20. PDF.
