Chapter 3: The Celti and the Getae
And Ptolemaeus, the son of Lagus, says that on this expedition the Celti who lived about the Adriatic joined Alexander for the sake of establishing friendship and hospitality, and that the king received them kindly and asked them when drinking what it was that they most feared, thinking they would say himself, but that they replied they feared no one, unless it were that Heaven might fall on them, although indeed they added that they put above everything else the friendship of such a man as he. And the following are signs of the straightforwardness of the barbarians: first, the fact that Syrmus refused to consent to the debarkation upon the island and yet sent gifts and made a compact of friendship; and, secondly, that the Celti said that they feared no one, and yet valued above everything else the friendship of great men.
Strabo. The Geography of Strabo English translation by Horace White. Vol. II. Cambridge, MA: Harvard University Press, 1988. Loeb Classical Library.