Snow was gathering in low spots, and the planet was freezing up.

The lines of solar distortion were strong, and they traced them to their
point of concentration. The point was not some isolated spot far in a
desert, away from Martian investigation. To the amazement of the men,
the location of the Sun-tap station was actually within a Martian city!

"Do you suppose," Lockhart queried the others, "that the Martians
themselves are the builders of this setup--that this is their
project--that they are the criminals and not the victims?"

There was no answer. The evidence was apparent, but it made no sense. If
the Martians had created this thing, it was destroying them. And yet, if
they had not created it, why did they--so clearly a race that had
attained a high level of engineering ability--tolerate its continual
existence?

As the ship descended, they saw the city emerge. It consisted of
hundreds of gray mounds--buildings laid out in the form of neat
hemispherical structures, like skyscraper igloos, with rows of circular
windows. Each building was like the next, and they fitted together in a
series of great circles, radiating outward from the meeting spot of the
canals.

The explorer crew waited at the ship's rocket launchers for an attack.
The tail of the teardrop housed the built-in armament--the rocket tubes
which could send forth destruction to an enemy. But though Haines sat
with his finger on the launcher button, no aircraft rose to meet them
from the city below. No guns barked at them. No panic started in the
streets.

They could see tiny dots of living beings moving about, but no sign of
alarm, no evidence that they had been noticed.

Even here, at the equator, there were streaks of white snow in the
streets and rings of rime along the bases of the buildings.

Directly below them lay the Sun-tap station. The lines converged here,
and the rings of distortion could be seen in the atmosphere, causing the
city to flicker as if from the presence of invisible waves.

Then they saw the masts and their shining accumulators projecting about
a cleared spot near the outskirts of the city. The customary walled
ring and the open machinery were not visible.

"The Sun-tap station is under the city!" said Lockhart, shocked. "It's
been built beneath the streets somewhere, and the Martians walk around
above it and let the masts alone! They must be the builders!"

"If so, why are they killing themselves?" Burl couldn't s