Persian troops denominated by Greek writers as κάρδακες appear infrequently in our sources for Achaemenid history, though they are recorded as having a substantial presence at Issus (333 BC). A comprehensive study of these troops is lacking and is of potentially great importance to our understanding of the military system of the Achaemenids, particularly after Xerxes' failed enterprise against Greece, and in light of the 10,000 Immortals' general disappearance from the literary record. Whether they were (a) light or heavy infantry and (b) mercenaries or native Persians has long been the subject of debate, with no particularly conclusive results. This study dismisses Strabo as a useful source on the κάρδακες, and attempts to reconcile the divergent source traditions of Arrian, who describes them as , and Callisthenes (recorded by Polybius), who writes of Persian πελτασταί at Issus. From an investigation of a wide variety of texts, together with lexicographical sources, it is possible to conclude that the hitherto enigmatic κάρδακες were general-purpose infantry not dissimilar to Iphicratean πελτασταί, and that, collectively, they constituted an ethnically diverse infantry force.