The Barbarians

The execution violated the basic laws of Tharnar. But the danger was too great—The Terrans couldn't be permitted to live under any circumstances....
Tal-Karanth, Supreme Executive of Tharnar, signed the paper and dropped it in to the out-going slot of the message dispatch tube. It was an act that would terminate one hundred and eighty days of studying the tapes and records on the Terran ship and would set the final hearing of the Terran man and woman for that day.
And, since the Terrans were guilty, their execution would take place before the sun rose again on Tharnar.
He went to the wide windows which had automatically opened with the coming of the day's warmth and looked out across the City. The City had a name, to be found in the books and tapes of history, but for fifty thousand years it had been known as the City. It was the city of all cities, the center and soul of Tharnarian civilization. It was a city of architectural beauty, of flowered gardens and landscaped parks, a city of five hundred centuries of learning, a city of eternal peace.
The gentle summer breeze brought the sweet scent of the flowering lana trees through the window and the familiar sound of the City as it went about its day's routine; a sound soft and unhurried, like a slow whisper. Peace for fifty thousand years; peace and the unhurried quiet. It would always be so for the City. The Supreme Executives of the past had been chosen for their ability to insure the safety of the City and so had he.
He turned away from the window and back to his desk, to brush his hand across the gleaming metal top of it. No faintest scratch marred the eternalloy surface, although the desk had been there for more than thirty thousand years. It was permanent and never-changing, like the robot-operated fleet that guarded Tharnar, like the white and massive Executive Building, like the way of life on Tharnar.
The Terrans would have to die, lest the peace and the way of life on Tharnar be destroyed. They were of a young race; a race so young that his desk had already been in place for fifteen thousand years when they began emerging from their caves. They were a dangerously immature race; it had been only three hundred years since their last war with themselves. Three hundred years—three normal Tharnarian lifetimes. And the Tharnarians had not known war for six hundred lifetimes.