‘One is on display in the Hall of Bears and Their Things. I suppose the others must be down here, somewhere.’

‘There are certainly a lot of them.’

The slabs, piled in stacks, leaning against pillars or propped upright, were carved with symbolic images of royalty seated on thrones before crowds of miniature subjects abasing themselves, riding oxen or crocodiles at the head of rivers of soldiers, blessing the sowing of crops and their harvest, sacrificing animals or prisoners of war or native slaves to their sun god.

They walked on. Darkness ahead, darkness behind, the lamp Ysbel held like a faint star drifting through the abyssal depths of an ocean of time. The labyrinth of stelae gave way to a store of artefacts from the new cities. Books and furniture and finely decorated pottery and glassware. Tapestries and intricately carved panels more varied and refined than any of the stelae. Huge mechanisms of wood and iron. A case of telescopes and sextants. A celestial globe …

Goodwill said that he had been taking note of the numbers on the pillars, and believed that they were close to their prize. ‘Do you hear running water? It is one of the streams channelled underground when the Library was built. What we are looking for is on the other side.’

The stream ran at the bottom of a channel lined with stone slabs; a bridge built of wood slats cunningly pieced together without need for nails, bolts or spikes arched above it. On the far side were rows of stone panels which had once decorated the chambers and terraces of bear cities. At first, they were all much the same size, as tall as Goodwill and about twice as long, and like the stelae they were incised with variations of the same few images. Stylised depictions of clashes between armies led by the giant figures of warrior kings, processions and courtly scenes, the sun god blazing through the sky in a chariot pulled by eagles, above the primeval flood which, according to myth, He had burned away to reveal the recreated world and the clay from which He had baked bears and their slaves and every kind of animal. Then Ysbel and Goodwill reached the section where panels from the new cities were stored, more finely carved and more various. Abstract patterns, images of animals and plants, teams of bears using levers and ramps to raise their iconic pyramids, bear artisans manufacturing pottery or glass, or hand-carving wooden blocks and using them in screw-presses to print books.

As he and Ysbel walked along a narrow aisle between two rows of these panels, Goodwill paid special attention to the numbers painted on the squat stone columns that supported the ceiling. They turned left, turned right, passed two more columns and stopped at a gap in one of the rows.

Goodwill studied the letter that Clarity Forrester had given him, turned in a circle. ‘It should be here,’ he said.