Spartans fought in a phalanx, cohesiveness was their strength. Not 1 vs 1 fighting. To not understand that is to completely be unbeknownst to what a spartan is.
I'd still give 1 spartan a fair chance against the gorilla. The gorilla would charge in, likely take a spear to the center of mass, it would continue charging likely to feel spartan sword steel.
These were extremely skilled swordsmen. They also knew how to move on the battle field, a gorilla would charge in a straight line. A spartan has more sophisticated maneuvers.
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The spartan dory (spear) was also 7 to 9 feet long. The gorilla would be speared long before it got in range of the spartan. At which point the spartan would take out his sword and wade in for the kill. Or simply hold position waiting for the gorilla to continue forward. But taking a 9 foot dory to the center of mass would have had slowed the gorillas assault.
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