It became clear to me that the Dvina went on and on, like a railroad track, whereas I had always supposed that it stopped where Polotzk stopped.

I had never seen the end of Polotzk; I meant to, when I was bigger.

But how could there be an end to Polotzk now?
Polotzk was everything on both sides of the Dvina, as all my life I had known; and the Dvina, it now turned out, never broke off at all.

It was very curious that the Dvina should remain the same, while Polotzk changed into Vitebsk! The mystery of this transmutation led to much fruitful thinking.

The boundary between Polotzk and the rest of the world was not, as I had supposed, a physical barrier, like the fence which divided our garden from the street.