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Strategic and tactical considerations

From a strategic point of view, the Athenians had some disadvantages at Marathon. In order to face the Persians in battle, the Athenians had to summon all available hoplites; even then they were still probably outnumbered at least 2 to 1. Furthermore, raising such a large army had denuded Athens of defenders, and thus any secondary attack in the Athenian rear would cut the army off from the city; and any direct attack on the city could not be defended against. Still further, defeat at Marathon would mean the complete defeat of Athens, since no other Athenian army existed. The Athenian strategy was therefore to keep the Persian army pinned down at Marathon, blocking both exits from the plain, and thus preventing themselves from being outmaneuvered. However, these disadvantages were balanced by some advantages. The Athenians initially had no need to seek battle, since they had managed to confine the Persians to the plain of Marathon. Furthermore, time worked in their favour, as every day brought the arrival of the Spartans closer. Having everything to lose by attacking, and much to gain by waiting, the Athenians remained on the defensive in the run up to the battle. Tactically, hoplites were vulnerable to attacks by cavalry, and since the Persians had substantial numbers of cavalry, this made any offensive maneuver by the Athenians even more of a risk, and thus reinforced the defensive strategy of the Athenians.

The Persian strategy, in contrast, was probably principally determined by tactical considerations. The Persian infantry was evidently lightly armoured, and no match for hoplites in a head-on confrontation (as would be demonstrated at the later battles of Thermopylae and Plataea.) Since the Athenians seem to have taken up a strong defensive position at Marathon, the Persian hesitance was probably a reluctance to attack the Athenians head-on. The camp of the Athenians was located on a spur of mount Agrieliki next to the plain of Marathon; remains of its fortifications are still visible.

Whatever event eventually triggered the battle, it obviously altered the strategic or tactical balance sufficiently to induce the Athenians to attack the Persians. If the first theory is correct (see above), then the absence of cavalry removed the main Athenian tactical disadvantage, and the threat of being outflanked made it imperative to attack. But if the second theory is correct, then the Athenians were merely reacting to the Persians attacking them. Since the Persian force obviously contained a high proportion of missile troops, a static defensive position would have made little sense for the Athenians; the strength of the hoplite was in the melee, and the sooner that could be brought about, the better, from the Athenian point of view. If the second theory is correct, this raises the further question of why the Persians, having hesitated for several days, then attacked. There may have been several strategic reasons for this; perhaps they were aware (or suspected) that the Athenians were expecting reinforcements. Alternatively, they may have felt the need to force some kind of victory—they could hardly remain at Marathon indefinitely.