yes to the barriers.

The wall here had been built higher than the portions which faced the
Flat, and it was stronger. No one had tried to storm the city from this
position, because it was too well protected. But the walls had been
built against the heavy, clumsy bodies of the grey aliens; with luck, a
man could scale this wall. The footholds in the weathered stones would
be precarious, but perhaps it could be done. And the Hirlaji, who
regarded this wall as impregnable, would not be guarding it.

Sighting upward from flat against the wall, he chose his path quickly,
and began to climb. The stone was smooth but grainy; he dug his fingers
into narrow niches and pulled himself slowly upward, bracing himself
with footholds whenever he could. It was laborious, painful work; twice
he lost handholds and hung precariously until his straining fingers
again found some indentation. Sweat covered him; the wind from the Flat
whipped around the wall and touched the moisture on his back coldly. But
his face was set in a frozen grimness and though his breath came in
gasps he made no other sound.

When he had neared the top he suddenly seemed to reach a dead-end; the
stones were smooth above him. His arms ached, his shoulders seemed
deadened; he clung numbly to the wall and searched for another path.
When he found it, he had to descend ten feet and move to the right
before he could re-ascend; as he retraced his route down the wall he
noticed blood where his torn fingers had left their mark. But he could
not feel the pain in his fingers.

At last, when the wall had come to seem a separate world of existence
which was all that he would ever know, a vertical plane to which he
clung with dim determination, hardly knowing why any longer ... at last,
he reached the top. His groping hand reached up and found the edge of
the wall; his fingers grasped it gratefully and he pulled himself up to
hang by both hands and survey the interior of the fortress.

A deserted floor stretched before him, shadowed by the late-afternoon
darkness which crept down from the mountains to rest on the aged remains
of the city. Forty feet down the walkway he saw stairs descending, but
his head swam and all he could focus on clearly was the light film of
dust and sand which covered even this topmost level of the city, blown
in shallow drifts against the walls which rose a few feet above the
floor here. There were no footprints in that dust; no one had walked
here