Datis, a Mede, commanded, along with Artaphernes, the Persian army that was defeated at Marathon, B.C. 490 ( Herod. vi. 94). (Harpers Dictionary of Classical Antiquities, 1898)

Medes were occasionally employed in high commands, Mazares (i. 156 f.) and Harpagus (i. 162 f.) by Cyrus, the sons of Datis (vii. 38) by Xerxes, and by Darius earlier in his reign, Tachamaspates, and Intaphres (Behist. Inscr. ii. 14. 6; iii. 14. 3). Here Datis is evidently in command; Artaphrenes, who was probably still young, seems to hold an honorary position. He is son (vii. 74) of Artaphrenes, brother of Darius, once satrap of Sardis (v. 25 f.). (How and Wells, A Commentary on Herodotus, 1928).