Why was Thermopylae a strategic victory?

Because the Greeks found an extremely narrow canyon, about 20 ft, where they fought knowing that the Persians could not suround them, so numbers would not be such a large factor. The Persians knew this, so before clashing sWords the rained upon them with arrows for one day straight, devistating the Greek army, then from the cliffs the tossed down boulders. later they found a passage around and surprised the Greek army from behind, destroying them. There were 3,000 Greek casualties and 2,000 Persian casualties in the end.