Jim Lacey is professor of strategic studies at the Marine War College and the author of a new history of the Battle of Marathon.

Before dawn on Sept. 12, 490 b.c., 10,000 mostly Athenian hoplites formed for an assault on the Persian force assembled before them on the Marathon Plain, nearly 25 miles from Athens. At the sound of a single trumpet, the advance began. Eight men deep on the flanks and four deep in the center, the phalanx of bristling spear points and blazing shields began its slow, inexorable march toward the enemy.

Picking up the pace, first to a fast walk and then to a trot, the Athenian hoplites closed on their enemy at what must have appeared to the waiting Persians a dazzling pace. At 600 yards’ distance the mass of men began to scream their fierce and nerve-shattering battle cry: Alleeee!

Hastily, the Persian commanders aligned their troops. Men holding wicker shields went to the front as thousands of archers arrayed themselves behind them. The Persian army showed no panic. They were professional soldiers, victors of a hundred bloody battles. In another moment their archers would release, and tens of thousands of deadly bolts would fill the sky. Afterward, the waiting spearmen would advance to slaughter the shattered and decimated remnants of the Greek force.

But the Persians had never before faced an army like this one…