The ancestors dropped away, sliding back down the pyramid as fast as they had climbed it, leaving Teppic alone on a few square feet of rock.

A couple of stars came out.

He saw white shapes below as the ancestors hurried away on some private errand of their own, lurching at a surprising speed towards the broad band of the river.

The gods abandoned their interest in Dios, this strange little human with the stick and the cracked voice. The nearest god, a crocodile-headed thing, jerked on to the plaza before the pyramid, squinted up at Teppic, and reached out towards him. Teppic fumbled for a knife, wondering what sort was appropriate for gods .

And, along the Djel, the pyramids began to flare their meagre store of hoarded time.

Priests and ancestors fled as the ground began to shake. Even the gods looked bewildered.

IIb snatched his father's arm and dragged him away.

'Come on!' he yelled into his ear. 'We can't be around here when it goes off! Otherwise you'll be put to bed on a coathanger!'

Around them several other pyramids struck their flares, thin and reedy affairs that were barely visible in the afterglow.

'Dad! I said we've got to go!'

Ptaclusp was dragged backwards across the flagstones, still staring at the hulking outline of the Great Pyramid.

'There's someone still there, look,' he said, and pointed to a figure alone on the plaza.

IIb peered into the gloom.

'It's only Dios, the high priest,' he said. 'I expect he's got some plan in mind, best not to meddle in the affairs of priests, now will you come on.'

The crocodile-headed god turned its snout back and forth, trying to focus on Teppic without the advantage of binocular vision. This close, its body was slightly transparent, as though someone had sketched in all the lines and got bored before it was time to do the shading. It trod on a small tomb, crushing it to powder.

A hand like a cluster of canoes with claws on hovered over Teppic. The pyramid trembled and the stone under his feet felt warm, but it resolutely forbore from any signs of wanting to flare.

The hand descended. Teppic sank on one knee and, out of desperation, raised the knife over his head in both hands.

The light glinted for a moment off the tip of the blade and then the Great Pyramid flared.

It did it in absolute silence to begin with, sending up a spire of eye-torturing flame that turned the whole kingdom into a criss-cross of black shadow and white light, a flame that might have turned any watchers not just into a pillar of salt but into a complete condiment set of their choice. It exploded like an unwound dandelion, silent as starlight, searing as a supernova.

Only after it had been bathing the necropolis in its impossible brilliance for several seconds did the sound come, and it was sound that winds itself up through the bones, creeps into every cell of the body, and tries with some success to turn them inside out. It was too loud to be called noise. There is sound so loud that it prevents itself from being heard, and this was that kind of sound.

Eventually it condescended to drop out of the cosmic scale and became, simply, the loudest noise anyone hearing it had ever experienced.

The noise stopped, filling the air with the dark metallic clang of sudden silence. The light went out, lancing the night with blue and purple afterimages. It was not the silence and darkness of conclusion but of pause, like the moment of equilibrium when a thrown ball runs out of acceleration but has yet to have gravity drawn to its attention and, for a brief moment, thinks that the worst is over.

This time it was heralded by a shrill whistling out of the clear sky and a swirl in the air that became a glow, became a flame, became a flare that sizzled downwards into the pyramid, punching into the mass of black marble. Fingers of lightning crackled out and grounded on the lesser tombs around it, so that serpents of white fire burned their way from pyramid to pyramid across the necropolis and the air filled with the stink of burning stone.

In the middle of the firestorm the Great Pyramid appeared to lift up a few inches, on a beam of incandescence, and turn through ninety degrees. This was almost certainly the special type of optical illusion which can take place even though noone is actually looking at it.

And then, with deceptive slowness and considerable dignity, it exploded.

It was almost too crass a word. What it did was this: it came apart ponderously into building-sized chunks which drifted gently away from one another, flying serenely out and over the necropolis. Several of them struck other pyramids, badly damaging them in a lazy, unselfconscious way, and then bounded on in silence until they ploughed to a halt behind a small mountain of rubble.

Only then did the boom come. It went on for quite along time.

Grey dust rolled over the kingdom.

Ptaclusp dragged himself upright and groped ahead, gingerly, until he walked into someone. He shuddered when he thought about the kind of people he'd seen walking around lately, but thought didn't come easily because something appeared to have hit him on the head recently .

'Is that you, lad?' he ventured.

'Is that you, dad?'

'Yes,' said Ptaclusp.

'It's me, dad.'

'I'm glad it's you, son.'

'Can you see anything?'

'No. It's all mist and fog.'

'Thank the gods for that, I thought it was me.'

'It is you, isn't it? You said.'

'Yes, dad.'

'Is your brother all right?'

'I've got him safe in my pocket, dad.'

'Good. So long as nothing's happened to him.'

They inched forward, clambering over lumps of masonry they could barely see.

'Something exploded, dad,' said IIb, slowly. 'I think it was the pyramid.'

Ptaclusp rubbed the top of his head, where two tons of flying rock had come within a sixteenth of an inch of fitting him for one of his own pyramids. 'It was that dodgy cement we bought from Merco the Ephebian, I expect-'

'I think this was a bit worse than a moody lintel, dad,' said IIb. 'In fact, I think it was a lot worse.'

'It looked a bit wossname, a bit on the sandy side-'

'I think you should find somewhere to sit down, dad,' said IIb, as kindly as possible. 'Here's Two-Ay. Hang on to him.'

He crept on alone, climbing over a slab of what felt very suspiciously like black marble. What he wanted, he decided, was a priest. They had to be useful for something, and this seemed the sort of time one might need one. For solace, or possibly, he felt obscurely, to beat their head in with a rock.

What he found instead was someone on their hands and knees, coughing. IIb helped him - it was definitely a him, he'd been briefly afraid it might be an it - and sat him on another lump of, yes, almost certainly marble.

'Are you a priest?' he said, fumbling in the rubble.

'I'm Dil. Chief embalmer,' the figure muttered.

'Ptaclusp IIb, paracosmic archi-' IIb began and then, suspecting that architects were not going to be too popular around here for a while, quickly corrected himself. 'I'm an engineer,' he said. 'Are you all right?'

'Don't know. What happened?'

'I think the pyramid exploded,' IIb volunteered.

'Are we dead?'

'I shouldn't think so. You're walking and talking, after all.'

Dil shivered. 'That's no guideline, take it from me. What's an engineer?'

'Oh, a builder of aqueducts,' said IIb quickly. 'They're the coming thing, you know.'

Dil stood up, a little shakily.

'I,' he said, 'need a drink. Let's find the river.'

They found Teppic first.

He was clinging to a small, truncated pyramid section that had made a moderate-sized crater when it landed.

'I know him,' said IIb. 'He's the lad who was on top of the pyramid. That's ridiculous, how could he survive that?'

'Why's there all corn sprouting out of it, too?' wondered Dil.

'I mean, perhaps there's some kind of effect if you're right in the centre of the flare, or something,' said IIb, thinking aloud. 'A sort of calm area or something, like in the middle of a whirlpool-' He reached instinctively for his wax tablet, and then stopped himself. Man was never intended to understand things he meddled with. 'Is he dead?' he said. 'Don't look at me,' said Dil, stepping back. He'd been running through his mind the alternative occupations now open to him. Upholstery sounded attractive. At least chairs didn't get up and walk after you'd stuffed them. IIb bent over the body.

'Look what he's got in his hand,' he said, gently bending back the fingers. 'It's a piece of melted metal. What's he got that for?'

Teppic dreamed.

He saw seven fat cows and seven thin cows, and one of them was riding a bicycle.

He saw some camels, singing, and the song straightened out the wrinkles in reality.

He saw a finger Write on the wall of a pyramid: Going forth is easy. Going back requires (cont. on next wall) . . .

He walked around the pyramid, where the finger continued: An effort of will, because it is much harder. Thank you.

Teppic considered this, and it occurred to him that there was one thing left to do which he had not done. He'd never known how to before, but now he could see that it was just numbers, arranged in a special way. Everything that was magical was just a way of describing the world in words it couldn't ignore.

He gave a grunt of effort.

There was a brief moment of speed. Dil and IIb looked around as long shafts of light sparkled through the mists and dust, turning the landscape into old gold.

And the sun came up.

The sergeant cautiously opened the hatch in the horse's belly. When the expected flurry of spears did not materialise he ordered Autocue to let out the rope ladder, climbed down it, and looked across the chill morning desert.

The new recruit followed him down and stood, hopping from one sandal to another, on sand that was nearly freezing now and would be frying by lunchtime.

'There,' said the sergeant, pointing, 'see the Tsortean lines, lad?'

'Looks like a row of wooden horses to me, sergeant,' said Autocue. 'The one on the end's on rockers.'

'That'll be the officers. Huh. Those Tsorteans must think we're simple.' The sergeant stamped some life into his legs, took a few breaths of fresh air, and walked back to the ladder.

'Come on, lad,' he said.

'Why've we got to go back up there?'

The sergeant paused, his foot on a rope rung.

'Use some common, laddie. They're not going to come and take our horses if they see us hanging around outside, are they? Stands to reason.'

'You sure they're going to come, then?' said Autocue. The sergeant frowned at him.

'Look, soldier,' he said, 'anyone bloody stupid enough to think we're going to drag a lot of horses full of soldiers back to our city is certainly daft enough to drag ours all the way back to theirs. QED.'

'QED, sarge?'

'It means get back up the bloody ladder, lad.'

Autocue saluted. 'Permission to be excused first, sarge?'

'Excused what?'

'Excused, sarge,' said Autocue, a shade desperately. 'I mean, it's a bit cramped in the horse, sarge, if you know what I mean.'

'You're going to have to learn a bit of will power if you want to stay in the horse soldiers, boy. You know that?'

'Yes, sarge,' said Autocue miserably.

'You've got one minute.'

'Thanks, sarge.'

When the hatch closed above him Autocue sidled over to one of the horse's massive legs and put it to a use for which it wasn't originally intended.

And it was while he was staring vaguely ahead, lost in that Zen-like contemplation which occurs at moments like this, that there was a faint pop in the air and an entire river valley opened up in front of him.

It's not the sort of thing that ought to happen to a thoughtful lad. Especially one who has to wash his own uniform.