^The Cambridge Ancient History, Volume 3, Part 2: The Assyrian and Babylonian Empires and Other States of the Near East, from the Eighth to the Sixth Centuries BC by John Boardman, I. E. S. Edwards, E. Sollberger, and N. G. L. Hammond,
ISBN0-521-22717-8, 1992, page 600: ";The Triballi were the western neighbours of the Treres and the Tilataei who occupied in general the region of Serdica"