'I am sure you are correct, arch magos, but nevertheless we should have a contingency plan. The Guard are but men. Flesh, blood and bone. Organic and therefore weak. They cannot be relied upon.'

'Yes, yes, you are right,' agreed Amaethon dreamily. 'The flesh is weak, Naicin. Only the machine is strong. We must not allow the laboratorium to fall into enemy hands.'

'As ever, your words are filled with wisdom, arch magos. But even as we speak the enemy drive towards the fastness of Tor Christo, and it is likely that it will fall within days.'

Amaethon's flaccid features twitched at this news, his eyes fluttering in sudden alarm.

'And the tunnel that links us to Tor Christo? Do the enemy know of it?'

'I do not believe so, arch magos, but should the Christo fall, it is inevitable that they will discover it.'

'They must not be allowed to make use of it!' trilled Amaethon.

'I agree, that is why I have armed the demolition charges that will destroy it.'

'Have you made Vauban aware of this?'

'No, arch magos.'

'Good. Vauban would not understand the necessity of such action. His compassion for his men would be our undoing.'

Amaethon seemed to sigh and was silent for some minutes before saying, 'I am… not as strong as once I was, Naicin. The burden I carry here is great.'

Magos Naicin bowed. 'Then allow me to bear some of that burden, arch magos. When the time comes that the enemy approach the inner walls of the citadel, you will be under immense strain to hold the energy shield in place as well as maintaining the citadel in working order. Allow some of that burden to fall upon my shoulders.'

Amaethon's skin mask nodded and with an abrupt change of subject the arch magos whispered, 'And what of the astropaths? Have you been able to isolate the contagion that afflicts them and renders their mind-voices mute?'

Momentarily taken aback, Naicin paused before answering. 'Ah, regrettably, no, but I am confident the answer lies within your logic stacks. It is just a matter of time before I am able to restore their abilities and once again send messages off-world.'

'Very good. It is imperative that we summon aid, Naicin. The magnitude of the consequences should we be defeated here is beyond imagination.'

'We shall not be defeated,' assured Magos Naicin with another bow.

On the morning of the eleventh day of the siege, Forrix's batteries were complete and the giant guns of the Iron Warriors were either dragged forwards by gangs of sweating slaves or rumbled along under their own diabolical power. Within minutes of the observers on the walls of Tor Christo spotting the movement of the giant artillery pieces, the Imperial Basilisks began firing, the endless barrage of shells turning the ground before the fortress into a hell of fire and shrapnel.

But the deepened and widened trenches were proof against all but direct hits, and only two machines were destroyed, their crews and those manhandling them shredded by lethal steel splinters. One massive gun, an ornate long-barrelled howitzer, was struck a glancing impact by a shell bursting directly overhead. Imbued with the bound energy of a daemon from the warp, the war machine screamed in lunatic fury, breaking free of its sorcerous bindings and running amok in the communication trench, crushing the four score slaves who pulled it and the guards who watched over it.

It took the combined efforts of Jharek Kelmaur, seven of his cabal sorcerers and the souls of a hundred slaves to placate the daemon, but soon, the gun was in its prepared position before the walls of Tor Christo.

The gunners on the walls attempted to shift their fire to the two batteries, realising that the chances of damaging the war machines traversing the trenches were slim, but Forrix had placed his batteries well and the Basilisks could not land their shells so close to the promontory.

It took another three deafening hours before Forrix was happy with the placement of his guns and the slaves shackled the daemonic war machines to the steel plates laid on the floor of the batteries.

At last, several hours after the sun had passed its zenith, Forrix gave the order to fire.

The first shells smashed into the south-eastern face of Kane bastion, throwing the men stationed on its walls to the ground. The rockcrete cracked under the impact, fist-sized chunks of grey rubble blasted skyward in a cloud of choking dust. It was followed seconds later by a volley from the second battery, smashing into the opposite face of the bastion.

This second volley was aimed high, blasting the top of the firing step clear in a storm of stone fragments that scythed men down by the dozen.

Blood and screams filled the air. Medics rushed to the aid of the wounded as their comrades dragged screaming soldiers from the walls to the courtyard below. Barely a minute had passed when yet more shells slammed into the walls of the Kane bastion, shaking it to its very foundations.

The noise was unbelievable. Major Tedeski knew that he would never forget the sheer, skull-pounding volume of the enemy bombardment. Each battery took it in turns to fire, the massive guns hurling explosive projectiles at his walls with incredible force. The stocky major had changed from his normal dress uniform and simply wore the standard issue sky blue jacket of the regiment, the one empty sleeve tucked inside. A flinching Captain Poulsen stood behind Tedeski, his face twitching with every crack of shell on stone.

Tedeski watched the corner gun tower crumble from the walls, carrying a dozen men screaming to their deaths on the rocks below.

'Upon my soul, it's bad,' he muttered.

'Sir?' enquired Poulsen.

'Nothing,' said Tedeski, scanning the walls. 'I want those men off the walls. Leave platoons one and five on the parapet and order all the others to withdraw.'

Poulsen relayed his commanding officer's order, grateful to have something to distract him from the thunderous shelling. Tedeski watched as the command filtered through to the walls, seeing the relief on the faces of the men ordered to withdraw and the fear of those who remained. The ground shook again as more shells impacted and Tedeski swore as an entire section of the southern wall cracked and crumbled to the base. Though the firing step was taking a punishing barrage, it would be some time before the enemy guns had pounded enough of the walls to form a practicable breach and brought down enough rubble for attacking troops to climb.

Stone splinters ripped through the bodies of the men who remained on the walls, tearing them to bloody rags, but Tedeski knew that he couldn't leave the walls totally unmanned for fear that an escalade was underway. There was every chance he was consigning these men to die, and the guilt of their deaths tasted like ashes in his mouth.

Suddenly, he set off towards the walls, climbing the dusty, fragment-strewn steps that led from the courtyard to the parapet.

'Sir?' shouted Poulsen, 'Where are you going?'

'To stand on the walls with my men,' snapped the irascible major.

Years of ingrained obedience kicked in and, without thinking, Poulsen trotted up the steps after Tedeski before his conscious brain truly understood what he was doing.

A ragged cheer greeted Tedeski's arrival as he marched to the head of the bastion, defiantly facing the enemy guns. The parapet here was cracked and sagging, several metres of rockcrete missing from its length, and Tedeski had a clear view of the scene below.

The two batteries were wreathed in clouds of thick grey smoke, which was periodically pierced by flashes of fire. Screaming projectiles slashed through the air as a soldier unnecessarily shouted, 'Incoming!'

The shells slammed into the base of the wall below Tedeski, blasting chunks of rock high into the air and enveloping him in a drifting bank of smoke. Tedeski didn't flinch and when the cloud cleared, merely dusted off his uniform jacket with his one hand.