He ate a little of the food, then strapped his pack in place.

He glanced up at the sun, determined this time to keep his bearings.

He walked south towards the mountains.

The pressure grew about him slowly, dragging him forward. As he watched the mountains they appeared to reduce in height. The substance of the soil on which he walked became thicker, and the terrain once more took on its appearance of fused lateral streaks.

Overhead, the sun moved faster than it had any right to do.

Fighting against the pressure, Helward stopped when he saw that the mountains were once again not much more than an undulating line of low hills.

He was not equipped to go further. He turned, and moved north. Night fell an hour later,

He walked on through the darkness until he felt the pressure was acceptably low, then rested.

When daylight came again, the mountains were clearly in view… and as mountains.

He made no attempt to move, but waited in his place. As the day advanced the pressure grew. He was being borne southwards by the motion of the ground towards the mountains… and as he watched and waited he saw them slowly spread laterally.

He moved camp, went northwards before night fell. He had seen enough; it was time to return to the city.

Unaccountably, the thought of this worried him. Would he have to make some kind of report on what had happened?

There was much he felt incapable of even absorbing into his own experience, let alone coalescing what he had seen and felt into a coherent order that he could describe to someone else.

At the centre of it all was the stupefying sight of the world spread before him. Had any man ever been privy to such an experience? How could the mind encompass a concept of which the eye had been incapable of seeing even the entire extent? To left and right — and, for all he knew, to the south of him — the surface of the world had extended seemingly without bound. Only in the north, due north, was there a definition of form: that curving, rising pinnacle of land which stretched to no visible end.

Likewise the sun, likewise the moon. And, for all he knew, likewise every body in the visible universe.

The three girls: how could he report on their safe conduct to their village when they had passed into a state in which he could not communicate with them, nor even see them? They had passed on into their own world, utterly alien to him.

The baby: what had happened to that? Manifestly of the city, for like him it had not been affected by the distortions that were otherwise all about them, presumably it had been abandoned by Rosario… and was now presumably dead. Even if it still lived, the motion of the ground would bear it southwards to that zone of pressure where it could not survive.

Lost in such thoughts, Helward walked on, taking little account of his surroundings. Only when he stopped to take a drink of water did he look about, and it was with a start of surprise that he realized that he recognized the terrain.

This was the rocky land to the north of the chasm where the bridge had been built.

He took a few mouthfuls of the water, then retraced his steps. If he was to find his way back to the city he must relocate the tracks, and the site of the bridge would be a better landmark than most.

He encountered a stream which, in his preoccupied state, he must have crossed without noticing. He followed its course, wondering if this could possibly be the same stream, for it appeared to be a tiny rivulet. In due time the banks of the stream became steeper and rougher, but there was no sign of the chasm.

Helward scrambled up the bank, and walked back against the direction of the water-flow. Though naggingly familiar, the appearance of the stream was distended and distorted, and it could be another stream entirely.

Then he noticed a long black oval near the edge of the water. He went down and examined it. There was a faint smell of burning… and on closer inspection he realized this was the scar of a fire. His camp-fire.

The stream next to it was no more than a yard wide, and yet when he had been here with the girls it had been at least twelve feet across. He went back to the top of the bank. After a long search he found some marks on the ground which could have been the traces of one of the suspension towers.

From the top of one bank to the next, the distance could have been no more than five or six yards. The drop to the water was a matter of feet.

At this point the city had crossed.

He walked northwards, and in a short while found the trace of a sleeper. It was about seventeen feet long. The one next to it was three inches away.

By the following night the scale of the landscape had assumed proportions that were more familiar to him. Trees looked like trees, not sprawling bushes. Pebbles were round, grass grew in clumps, not spread like a smear of green. The tracks by which he walked were still too widely spread to have any resemblance to the gauge used by the city, but Helward thought that his journey should not be much longer.

He had lost track of the number of days that had passed, but the terrain was becoming increasingly familiar to him, and he knew that so far his time away from the city was still considerably less than that predicted by Clausewitz. Even taking into account the two or three days that had seemed to pass so quickly while he was in the zone of pressure, the city could not have moved more than a mile or two further to the north while he was away.

This thought encouraged him, for his supplies of food and water were dwindling.

He walked on, and the days passed. There was still no sign of the city, and the tracks by which he walked showed no signs of narrowing to their more normal gauge. By now he was so accustomed to the notion of the lateral distortion of this world in the south, that he took the evidence of it much in his stride.

One morning, he was disturbed by a new thought: for several days the gauge of the tracks had not appeared to change, and could it be that he had encountered a region where the motion of the ground was directly equal to the speed of his own walking? That is, that he was like a mouse on a treadmill, never making any forward progress?

For an hour or two he hastened his walk, but soon reason prevailed. He had, after all, successfully moved away from the zone of pressure where the southward motion was greater. But more days passed, and the city seemed to be no nearer. Soon he was down to his last two packets of food, and twice he had had to supplement his water-supplies from local sources.

The day he reached the end of his food, he was suddenly taken by a surge of excitement. Potential starvation was no longer a problem… he had recognized where he was! This was the region he had been riding through with Barter Collings: at that time, two or three miles north of optimum!

By his estimate of time he had been gone for three miles at the most… so the city should be in sight.

Up ahead, the line of track-scars continued until a low ridge… and no sign of the city. The sleeper-pits were still distorted, and the next row of scars — the left inner — was some distance away.

All it could mean, Helward reasoned, was that while he was away the city had somehow moved much faster. Perhaps it had even overtaken the optimum, and was in a region where the ground moved more slowly. Already he was beginning to understand why the city moved on: perhaps ahead of optimum there was a zone where the ground did not move at all.

In which case the city could stop… the grand treadmill would end.