Most of the troopers’ heads were crudely shaved, a practicality if you were doomed to wear your skinsuit without a break for days at a time. With grime etched deep into their pores it was impossible to tell how old they were. They looked tired, and yet kept on with their work even so, long past the normal limits of humanity. They were nothing like the steel-eyed warriors Luca had imagined. They looked like experts in nothing but endurance.

It seemed to Luca that what they were basically doing was digging. Many of them used simple shovels, or even their bare hands. They dug trenches and pits and holes, and excavated underground chambers, each trooper, empowered by microgravity, hauling out huge masses of crumpled rock. Luca imagined this scene repeated on a tremendous swarm of these drifting rocky worldlets, soldiers digging endlessly into the dirt, as if they were constructing a single vast trench that enclosed the Galaxy Core itself.

Dolo made a remark about the patched-up suits.

Teel shrugged. ‘Suits are expensive here. Troopers themselves are cheaper.’

Luca said, ‘I don’t understand why they are digging holes in the ground.’

‘To save their lives,’ Teel said.

‘It’s called “riding the Rock”, Novice,’ Dolo said.

When it was prepared, Luca learned, this asteroid would be thrown out of its parent system, and in through the Molecular Ring towards the Xeelee concentrations. The first phase of the journey would be powered, but after that the Rock would fall freely. The troopers, cowering in their holes in the ground, would ‘run silent’, as they called it, operating only the feeblest power sources, making as little noise and vibration as possible. The point was to fool the Xeelee into thinking that this was a harmless piece of debris, and for cover many unoccupied rocks would be hurled in along similar trajectories. At closest approach to a Xeelee emplacement - a ‘Sugar Lump’ - the troopers would burst out of their hides and begin their assault.

‘It sounds a crude tactic, but it works,’ said Dolo.

‘But the Xeelee hit back,’ said Luca.

‘Oh, yes,’ Teel said, ‘the Xeelee hit back. The rocks themselves generally survive. Each time a rock returns we have to dig out the rubble, and build the trenches and shelters again. And bury the dead.’

Luca frowned. ‘But why dig by hand? Surely it would be much more efficient to leave it to the machines.’

Dolo said carefully, ‘The soldiers seem to believe that a shelter constructed by a machine will never be as safe as one you have dug out yourself.’

‘That doesn’t make sense,’ Luca said. ‘All that matters is a shelter’s depth, its structural qualities—’

‘We aren’t talking about sense,’ Dolo said. ‘We are touching here on the problem we have come to study. Come, Novice; recall your studies on compensatory belief systems.’

Luca had to dredge up the word from memory. ‘Oh. Superstition. The troopers are superstitious.’