“Not enough air,” he said. He spoke English, with a faint American twang remaining after generations. They were chiefly Americans who went to Sibylla. “We’re about as high on this massif as we can go.”

“But…oh, yes,” I recalled. “The pressure gradient’s steeper than on Earth. Your planet’s got fifty percent more diameter, a third more surface gravity.”

“And less air to start with.” Brenner cleared his throat. I recognized the preliminary to a speech.

“We leave the lowlands be because they’re too hot, not because of too thick an atmosphere,” he said. “Remember, this is a metal-poor globe, lowish density in spite of its mass. So it didn’t outgas as much as it might have, in the beginning. Also, on account of the slow rotation, it don’t have any magnetic field worth mentioning. Cumae may not be the liveliest star in the universe, but it does spit plenty protons and photons and stuff to thin out an atmosphere that hasn’t got a magnetic field to hide behind. We get a pretty strong radiation background too for the same reason; gives medical problems, and it’d be worse higher up. Furthermore, when you got an extra ought-point-three gee on you, and manual labor to do, you need lots of oxygen. So the long and the short of it is, we can’t colonize the real heights.” He cocked his head at me. “Didn’t they brief you ay-tall, son?”

I looked back at him hard, feeling I rated more respect as the first officer of an exploratory ship. His leathery features crinkled in a slow grin. The President of Sibylla was no more formal than the rest of his ten thousand people.

He wore the usual archaic kilts, blouse, boots, sun helmet set rakishly on his grizzled head, machete at hip. But my uniform was less neat than his garb, ten minutes after we had left the buggy by the roadside and started climbing. The gravity didn’t bother me; we use rougher accelerations on a craft like the Bering. I was aware of my flesh and bones dragging downward, nothing worse. The heat, though, the booming and thrusting wind, the scanted lungfuls I breathed, dryness afire in nose and throat, malignant grab of branches and slither of sandy soil, something faintly intoxicant about the plant odors, had entered me. I was sweat-drenched, dusty, a-gasp and a-tremble, and gladder than I should be of a chance to rest.

I decided not to stand on the dignity I didn’t have. Besides, I thought, we were men together in the face of the not human. It had killed, it could kill again, it could smite Earth herself. I felt lonelier in that wide grim landscape than ever between the stars.

“They gave us what information was available,” I said. “But it was simultaneously too ample—for one head to contain—and too little—for the totality of a world. Hard for us to guess what’s significant and what’s incidental. And you’ve been isolated from us for nearly two centuries. Nothing but a thread of laser contact, with a third of each century needed to cross the distance between. Our fleet took longer still, of course; the big ships aren’t meant to go above one gee, so they need a year to approach light speed and another year to decelerate. Inboard time at minimum tau factor isn’t negligible either. We experienced several months in covering those parsecs. And we were wondering the whole way if we’d arrive to find the aliens had returned—arrive to find you dead here and a trap set for us. Under the circumstances, sir, we were bound to forget some of what we’d learned.”