Free Departures by Harry Turtledove Page A

any rate. Did I ever tell you that I studied medicine under Diodoros of Alexandria?”
    There were times when Tero found his friend’s evasiveness maddening. This, it seemed, was going to be one of them. “No,” he said, “you never did. Why do you see fit to impart this bit of information to me now?”
    “I am coming to that, never fear. You see, Diodoros himself was learning his skill in Alexandria when Heron son of Ktesibios was at the height of his fame.”
    Tero had to admit he did not know the name.
    “Do you not? A pity; he was a remarkable man, probably one of the finest machine makers the world has ever seen. Diodoros was fascinated by his contraptions, and he never tired oftalking about them. Really amazing things: a device for dispensing sacramental water that worked only when a copper was inserted, a trumpet made to sound by opening a nearby door, bronze animals that moved like live ones, and many other things.”
    “He sounds like a sorcerer.”
    “No, he was an artificer and nothing more. One of the things he made, not really more than a toy, was what he called an aeolipile.”
    “All of this must lead somewhere, I suppose. What might an aeolipile be?”
    Kleandros explained: a water-filled cauldron was fitted atop with a hollow ball mounted on a hollow tube. Directly opposite the tube’s entrance into the ball was a pivot, which was attached to the cauldron’s lid. The ball itself was fitted with bent nozzles; when a fire was lit beneath the cauldron, steam traveled up the hollow tube and out through the nozzles, making the ball spin merrily. “Do you see what I’m getting at?” the doctor asked. “In this device the force of the steam escaped continuously, but if some way were found to block it up for a time and then release it all at once, it could give a little metal pellet a very strong push indeed.”
    Tero took another pull at his wine while he thought. The idea had more than a little appeal, for it gave a rational picture of how the killing might have taken place. Still … “A cauldron, you say. How big a cauldron?”
    “I have no idea. I’ve never seen the machine in action myself, only heard Diodoros talk about it.”
    “Somehow I find it hard to imagine Clodius Eprius letting anyone set up a cauldron in the middle of the room and then aim a little ball at him. And whoever would be using it would have to wait for his water to boil before it would go off, wouldn’t he?”
    “I suppose so,” Kleandros said sulkily.
    “Not only that, anyone hauling a cauldron through the middle of Vesunna would get himself noticed. Even if I don’t know what killed Eprius, I can tell you a couple of things about it: you can use it right away, and you can carry it around without having it seen. I’m afraid your whatever-you-call-it misses the mark both ways.” Seeing his friend’s hurt expression, Tero went on. “If you could make one big enough, it might make a good ballista, though.” I wonder why our generals never thought of anything like that, he thought, a little surprised at himself.
    “Your logic is convincing,” Kleandros said, adding, “Damn it!” a moment later.
    “Let’s give up on the weapon for now,” Tero suggested. “It matters less than the person who used it. If we had some way of knowing who he was, we might catch him, thunderbolt thrower or no.”
    “A good point,” Kleandros said. “Whoever he was, we can be fairly sure he was from outside the empire.”
    “Why do you say that?”
    “We know of no weapons to fit the bill within our land, do we? Also, why would a citizen need to carry coins that weren’t genuine but would pass one by one? If they are true gold, that only makes the argument stronger.”
    “A spy!”
    “You may have something there. But who would want to spy on Vesunna, and why?”
    Tero opened his mouth for a reply, then realized he did not have a good one. No one had ever seen a German in the town, and Parthia was at the other end of the