The sun rose slowly, as if it wasn’t sure it was worth all the effort.

Another Disc day dawned, but very gradually, and this is why.

When light encounters a strong magical field it loses ail sense of urgency. It slows right down. And on the Discworld the magic was embarrassingly strong, which meant that the soft yellow light of dawn flowed over the sleeping landscape like the caress of a gentle lover or, as some would have it, like golden syrup. It paused to fill up valleys. It piled up against mountain ranges. When it reached Cori Celesti, the ten mile spire of grey stone and green ice that marked the hub of the Disc and was the home of its gods, it built up in heaps until it finally crashed in great lazy tsunami as silent as velvet, across the dark landscape beyond.

It was a sight to be seen on no other world.

Of course, no other world was carried through the starry infinity on the backs of four giant elephants, who A’ere themselves perched on the shell of a giant turtle. His name—or Her name, according to another school of thought—was Great A’Tuin; he—or, as it might be, she—will not take a central role in what follows but it is vital to an understanding of the Disc that he—or she—is there, down below the mines and sea ooze and fake fossil bones put there by a Creator with nothing better to do than upset archeologists and give them silly ideas.

Great A’Tuin the star turtle, shell frosted with frozen methane, pitted with meteor craters, and scoured with asteroidal dust. Great A’Tuin, with eyes like ancient seas and a brain the size of a continent through which thoughts moved like little glittering glaciers. Great A’Tuin of the great slow sad flippers and star-polished carapace, labouring through the galactic night under the weight of the Disc. As large as worlds. As old as Time. As patient as a brick.

Actually, the philosophers have got it all wrong. Great A’Tuin is in fact having a great time.