Guardians of the Tower

Jon didn't know why he held a sword in his hand to fend off the Wild Ones; he knew only that he was one of many who for centuries had become—
That morning, the sun rose bright and clear over the Tower. Jon woke, clambered to his feet, and rolled his sleeping-blanket. Within five minutes, he was fully awake and ready to protect the Tower against its enemies.
He took his station and stared out over the sea. Far in the distance, he could make out the bomb-blackened city; off to the left was the spot of green that indicated the village of the Free People. Somewhere beyond were the lands of the Wild Ones—the ones Jon was here to defend the tower against.
All well to the East! he cried, when his turn came. The other Guardsmen, stationed in a circle around the Tower, called off their observations in turn.
The morning passed slowly. A little before noon, the man at the top of the Tower cried, Enemy boat approaching! Prepare to defend the Tower!
Jon's mouth tightened, and he squinted toward the dot of light on the sea that was the boat of the Wild Ones. Slowly, he drew his sword, whisked it through the air a few times, loosened his wrist. It was the first time in over a month that he had been called upon to do battle in the name of the Tower.
From within the Tower, the auxiliary guard-force came running out and took battle-stations. They stood ready, waiting for the Wild Ones to come.
No one knew what the Tower was. It had been there as long as any of the Free People could remember, and probably had been there forever. It was sacred to them, and for that reason was under constant attack by their enemies from the Wild Places.
At twenty-three, Jon had been a Tower guard for nearly three years, had taken part in almost twenty defenses. The Wild Ones had practically captured the Tower twice, but each time the guardians had driven them off.
Now, they were back for another try. Jon waited tensely as they drew near.
Time passed slowly. Five minutes, ten, while the enemy attacking-party approached. The look-out at the top of the Tower sang out periodically, keeping the guards below informed of the boat's progress.