“And the optimum is always moving?”

“No. The optimum is stationary… but the ground moves away from it.”

“Oh yes.”

We packed our gear and continued northwards. Just before sunset we made camp for the night.

4

The surveying work was undemanding mentally, and as we moved slowly northwards I found that my only external preoccupation was a need to be ever-watchful for signs of hostile inhabitants. Denton told me that an attack on us was unlikely, but nevertheless we were on our guard.

I was still thinking about the awesome experience of seeing the whole world lying before me. As an event, it was enough; understanding it was something else.

On our third day out from the city I suddenly started to think about the education I had been given as a child. I’m not sure what started the train of thought; it was possibly a number of things, not least the shock of seeing how utterly the crèche had been destroyed.

I had thought little of my education since leaving the crèche. At the time I had felt, in common with most of the children in the crèche, that the teaching we were given was not much more than a penance, in which time was served as of necessity. But looking back, much of the education pushed into our unwilling heads took on a new dimension in the context of the city.

For instance, one of the subjects which had inspired in us the most boredom was what the teachers referred to as “geography.” Most of these lessons had been concerned with the techniques of cartography and surveying; in the enclosed environment of the crèche, such exercises had been almost wholly theoretical. Now, though, those hours of tedium took on their relevance at long last. With a little concentration and a certain amount of digging into my often faulty memory, I grasped quickly the principles of the work Denton was showing me.

We had had many other subjects taught to us theoretically, and I saw now how those too had practical relevance. Any new guild apprentice would already have a background knowledge of the work his own guild would expect him to do, and in addition would have similar information about many of the other functions of the city.

Nothing could have prepared me for the sheer physical grind of working on the tracks, but I’d had an almost instinctive understanding of the actual machinery used to haul the city along those tracks.

I cared not at all for the compulsory training with the Militia, but the puzzling — at the time — emphasis placed on military strategy during our education would clearly help those men who later took arms for the security of the city.

This process of thought led me to wonder whether there had been anything in my education that could possibly have prepared me for the sight of a world which was shaped the way this one appeared to be.

The lessons we had been given which specifically referred to astrophysics and astronomy had always spoken of planets as spheres. Earth — the planet, not our city — was described as an oblate spheroid, and we had been shown maps of some of its land surface area. This aspect of physical science was not dwelt upon; I’d grown up to assume that the world on which Earth city existed was a sphere like Earth planet, and nothing I had been taught had contradicted this assumption. Indeed, the nature of the world was never discussed openly at all.

I knew that Earth planet was part of a system of planets, which were orbiting a spherical sun. Earth planet itself was circled by a spherical satellite. Again, this information seemed always to be theoretical… and this lack of practical application had not concerned me even when I left the city, for it was always clear that a different circumstance obtained. The sun and moon were not spherical, and neither was the world on which we lived.

The question remained: where were we?

The solution lay perhaps in the past.

This too had been covered comprehensively, although the histories we were taught were exclusively about Earth planet. Much of what we learned concerned military manoeuvres, the transference of power and government from one state to another. We knew that time was measured in terms of years and centuries on Earth planet, that recorded history existed for about twenty centuries. Perhaps unfairly, I formed an impression that I should not care to live on Earth planet, as most of its existence seemed to be a series of disputes, wars, ter1itorial claims, economic pressures. The concept of civilization was far advanced, and explained to us as the state in which mankind congregated within cities. By definition, we of Earth city were civilized, but there seemed to be no resemblance between our existence and theirs. Civilization on Earth planet was equated with selfishness and greed; those people who lived in a civilized state exploited those who did not. There were shortages of vital commodities on Earth planet, and the people in the civilized nations were able to monopolize those commodities by reason of their greater economic strength. This imbalance appeared to be at the root of the disputes.

I suddenly saw parallels between our civilization and theirs. The city was undoubtedly on a war footing as a result of the situation with the tooks, and that in its turn was a product of our barter system. We did not exploit them through wealth, but we had a surplus of the commodities in short supply on Earth planet: food, fuel energy, raw materials. Our shortage was manpower, and we paid for that with our surplus commodities.

The process was inverted, but the product was the same.

Following my line of reasoning, I saw that the examination of the history of Earth planet prepared the way for those who would become Barter guildsmen, but it took me no further along my own search for understanding. The histories began and ended on Earth planet, with no mention of how the city came to be on this world, nor how the city had been built, nor about who its founders were and where they came from.

A deliberate omission? Or forgotten knowledge?

I imagined that many guildsmen had tried to construct their own patterns of logic, and for all I knew either the answers were available somewhere in the city, or there was a commonly accepted hypothesis which I had not yet encountered. But I had fallen naturally into the ways of the guildsmen. Survival on this world was a matter of initiative: on the grand scale, by hauling the city northwards away from that zone of amazing distortion behind us, and on the personal scale by deriving for oneself a pattern of life that was self-determined. Future Denton was a self-sufficient man, and so had been most of those I had met. I wanted to be one with them, and comprehend things on my own account. I supposed that I could discuss my thoughts with Denton, but I chose not to.

The journey northwards was slow and meandering. We did not take a route due north, but followed many diversions to east and west. Periodically Denton would measure our position against optimum, and never at any time were we further north than about fifteen miles.

I asked him if there were any reason why we should not strike even further north of optimum.

“Normally, we would go as far north as we can,” he said. “But the city’s in a special circumstance. As well as seeking the easiest northwards route, we need terrain that will allow us to defend ourselves best.”

The map we were compiling was becoming more complete and detailed every day. Denton allowed me to operate the equipment whenever I wished, and soon I was as adept as he. I learned how to triangulate the land with the surveying instrument, how to estimate the elevation of hills, and how to calculate the distance we were north or south of optimum. I was growing to like working the camera, in spite of the fact I was forced to curb my enthusiasm to conserve the energy in the batteries.