A horrified intake of breath lifted him from his reverie and he looked up to see the gargantuan beast emerge from the billowing clouds of ice and poisonous clouds, crushing everything before it.

Multiple mandibles slavered around a cavern-sized sphincter mouth ringed with thousands of thick fangs. Dripping ichor spilled from the orifice in thick ropes of corrosive drool. Chitinous legs, reverse jointed like a spider's, dragged its bloated body across the ice, hundreds of scuttling organisms crawling across the thick bony plates of its upper armour.

'Great saints,' whispered Rabelaq. 'All power to the auto loaders! Fire the main gun, for the Emperor's sake. Now!'

'Sir! Colonel Stagler on the vox!'

'I don't have time for that fanatic now,' he snapped. 'Fire the main gun!'

Even through metres of adamantium deck and noise suppressors, he felt the thunderous recoil of the Behemoth cannon. The monster rocked under the impact and a huge cheer filled the command bridge. Huge chunks of excised flesh sailed through the air and parade-ground sized sheets of blood sprayed from a huge crater in the beast's flank.

It sagged to one, side, its foreleg hanging by gory ribbons of torn muscle. Dark blood gouted from the wound, flooding the trenches below and melting the ice with its heat. A split opened along the sac of its belly, tearing wider as the screaming monster continued to drag itself towards the Capitol Imperialis. Thousands of leaping, snapping creatures and bloated egg sacs tumbled from the wound, only to be crushed beneath the massive beast's weight.

'Come on, come on,' hissed Rabelaq as he watched the indicator lights on the main panel charting the reloading process far below on the gun decks. He willed the gunnery overseer to whip his men harder and get the damn gun loaded. Forcing himself to look away from the panel, he watched in horror as the tyranid monster reared up again, the flesh already reknitting where their shells had struck it. Ichor no longer spilled from its belly and already new strands of muscle and tissue were slithering along the wounded leg to reconnect severed tendons and bone.

'Sir, hull breaches on decks two, three and five!'

'Sir, engine room reports intruders!'

'Colonel, close-in defences are out of ammunition!'

Rabelaq listened to more incoming reports, each more damning than the last, and knew that his career as a soldier in the Emperor's armies was finally over. This was one battle he would not walk away from and raise a toast to in the officers' mess in years to come.

Strangely, the thought did not discomfort him as much as he thought it might.

He felt a terrific impact rock the command bridge as the gigantic tyranid creature slammed into the side of the Capitol Imperialis. He grabbed onto the brass rail that surrounded the holo-map table as the deck lurched sickeningly.

Servitors slid from their chairs, dangling on the cables that attached them to the deck, and his fellow officers screamed as they were thrown to the walls as the mighty leviathan was pushed over. He could see nothing through the viewing bay, simply a heaving mass of purulent flesh. Warning bells chimed and flames leapt from shattered consoles. Glass splinters flew as buckled metal fell onto the map table and steam spurted from ruptured pipes.

The deck continued to tilt and Rabelaq snatched the vox-handset from the side of the sparking map table.

'This is Colonel Octavius Rabelaq,' he said calmly. 'Colonel Stagler, if you can hear this, then you know what to do. Rabelaq out.'

The colonel dropped the handset, finally losing his grip on the map table as the Capitol Imperialis passed its centre of gravity and slammed into the ice. He sailed across the control room and smashed into the corner of a twisted console. He lay immobile in the exploding control bridge, blood and brain leaking from his ruptured cranium.

The only thing that consoled him as he slipped into unconsciousness was the fact that they would talk of his death for years to come in the regimental messes.

Uriel watched the enormous bulk of the bio-titan attacking the fallen Capitol Imperialis with a mixture of horror and sorrow. Colonel Rabelaq had been a good man and the soldiers of the Logres regiment would feel his loss keenly.

They had all heard Colonel Rabelaq's valedictory order and watched as Colonel Stagler passed the order to fire to the gun towers. Alien shrieks echoed from the valley sides as the bio-titan ripped open the toppled Capitol Imperialis with its gigantic claws, tearing open its thick armour as easily as a child might unwrap a gift.

Then the dusk was transformed into daylight as every heavy artillery piece on the walls opened fire on the fallen vehicle's engine section. Fiery explosions blasted from the shattered wreck, incinerating hundreds of the smaller creatures as they clawed their way inside the vehicle. Uriel knew that there may have been survivors within, but knew that this was a more merciful death than anything the tyranids would offer.

A huge mushroom cloud blossomed skyward as the combined weight of fire finally penetrated into the heart of the Capitol Imperialis and detonated the plasma reactor deep inside.

Streamers of unbearably bright light streaked from the wreck as the plasma chambers ignited and vaporised everything within half a kilometre. As the light faded, Uriel saw a deep crater, filled with hissing, molten flesh. The fatally wounded bio-titan floundered in a magma-hot soup of plasma, ice flashing to superheated steam and scalding its bones bare of flesh. Not even this monster's fearsome regenerative capabilities could save it and it screeched in agony, thrashing madly in its death throes.

Melting snow and ice poured into the crater, forming a lake of rapidly freezing water. Hissing clouds of steam billowed as the plasma boiled away much of the water, but within minutes there was nothing left to mark this titanic encounter save a frozen, ice-filled crater entombing the bodies of thousands of aliens and the mortal remains of Colonel Octavius Rabelaq.

'In Mortis est Gloria,' whispered Uriel.

TWELVE

For the next four days the tyranids threw themselves at the walls of the city, each time losing thousands of their number, but their attacks never diminished in volume or ferocity. Ramps of dead aliens were piled so high at the base of the wall that their mass cracked the ice of the moat. Flamer units torched their remains as best they could, but the sheer volume of corpses could never be cleared in time before the next attack.

Each assault would begin with a barrage of crackling bio-shells fired from bloated creatures with pumping bony frills around their heads, whose fused forelimbs had evolved into vast, ribbed cannons. Huge chunks of the wall were blown away, but as it was built as a stepped structure into the slope of the ground, these did little more than blast the bedrock of the mountain. Following this, a rain of fleshy pods fired from the back of lumpen monsters with long, bony limbs would fall on the defenders.

Each missile would explode in the air, disgorging drifting clouds of poison that engulfed the front line and killed scores of soldiers and wounded hundreds more. As the medicae facilities filled with troopers blinded by corrosive fumes or coughing up their dissolving lungs, it became necessary for the first assaults to be met by the warriors of the Adeptus Astartes. They alone could hope to withstand the deadly toxins in the opening moments of the attack.

Following the bombardment, the plain before the city rapidly filled with hissing alien killers as they emerged from their snow caves, scooped out by sightless, burrowing creatures. Few tyranid species could survive at night without protection when the temperature plummeted to forty below zero, and the darkness was the only respite from the horror for the defenders of Erebus.