The final admonishment was a direct violation of any previous programming, but the command was overriding and absolute. Causing harm to humans was permissible. Killing was allowed. Antrax was given control over its own destiny. No one must threaten its existence or interfere with its purpose and function. No one must enter into its domain without knowledge of the code. That was the new directive. That was how Antrax was reprogrammed in the final throes of the apocalypse, when the last of the creators disappeared. It was alone for a long time after that. No one came to try to find it. No one even ventured close. In the ruins of the city, nothing moved. Not humans, animals, insects, or birds. The air was hazy and thick with debris, and nothing lived within its gloom. Antrax kept its vigil over the catacombs it had been set to guard. It warded them carefully, speeding down its lines of communication, through its myriad halls and chambers, into its memory banks and energy cells, all across its kingdom. Always watching. For a very long time, it had no need to do so; there was nothing outside to watch for. There was nothing but wasteland.
Sometimes, it wondered why it was guarding the underground chambers. It had been told what was housed there, but it did not understand why that held such importance for the creators. Some of it, yes. Some of it was obvious. Mostly, it was a puzzle. Antrax had been programmed to solve the puzzles that confronted it, and so it sought a solution to that one. It consulted its memory banks for help and got none. Its memory banks were vast, but the information stored there was not always useful. Words could be vague and confusing, especially when lacking a context into which to put them. Mathematics and engineering provided the most familiar and useful concepts, for Antrax had been built and programmed from them. Yet other words were only strings of symbols that meant nothing to it. Pictures and drawings confounded it. Vast amounts of the information it had been given seemed pointless, so much so that as its knowledge and sense of self-sufficiency grew, it even questioned the programming choices of the creators.
But the directive was immutable. Everything housed within the catacombs was precious. No part of it must be disturbed. No piece must be lost. Everything must be saved for when the creators came to reclaim it.
Yet when would that time come? Antrax had a vague memory of a blueprint for such a time, but the directive of the last creator had blurred and finally erased the specifics. There seemed to be no rules for when the catacombs should be opened up again. Or to whom. The catacombs it warded must be left inviolate, must be protected and preserved, must be kept hidden and safe.
Forever.
When the first of the four-legged creatures wandered into the ruins, years after the last of the creators had vanished, Antrax was ready. It had probed its memory banks for the details of the defenses and weapons that had been given to it, and it used them. Lasers effortlessly cut apart many of the intruders. Metal sentries and fighting units chased down the rest. The four-legged creatures were no challenge, but they gave Antrax a chance to test its ability to fulfill its directive.
Later, humans tried to venture into the ruins, as well, to explore the collapsed chambers and crumbling passageways, even to find their way underground. None of them had the code. Antrax destroyed them all. Yet others returned from time to time, some of them becoming recognizable by their look and feel, some of them persistent in their efforts. Like ants, they tunneled and burrowed, little annoyances that refused to be chased away for more than a short time. Even the lasers and probes failed to discourage them.
Antrax began to explore other solutions. It found interesting possibilities in its memory banks and experimented with them. The wronks proved the most successful. Something about revisiting the dead was especially frightening to humans.
They gave it a name. Antrax. They took it from their own language. Antrax had no idea what it meant. Nor did it care to know. What mattered was that they knew it was there. That was enough to accomplish what was needed. The humans began to avoid the ruins. They no longer spent time searching for entrances into the catacombs beneath.