Laden with tonnes of earth and rock, they plied their stately way up the ramp before depositing their cargo on its forward slope and then turning around and making their way back down again to refill. Millions of tonnes had already been poured out, yet the ramp was barely halfway towards the upper levels of the fortress. Uriel watched as a trio of bulk-haulers made their way towards the bottom of the ramp, and turned to Pasanius.

'They're coming,' he whispered through his armour's vox unit.

'I see them,' confirmed Vaanes.

Across the construction site from Uriel, he could see Vaanes climbing the side of the ramp, gaining height from where he could use his jump pack to better effect. Other Space Marines were poised ready for the word to attack.

The first of the bulk-haulers completed its wide turn and ground off into the smoke for more earth and Uriel bit his lip in nervous anticipation.

'Second one's almost round,' said Pasanius, and Uriel could sense the anticipation in his sergeant's voice.

'Aye,' he nodded. 'Ready?'

'As I'll ever be.'

'At times like this, I wish Idaeus was still here,' said Uriel.

Pasanius chuckled and said, 'This attack would be just his kind of thing.'

'What? Against impossible odds and with no recourse to the Codex Astartes?'

'Precisely,' said Pasanius, nodding in the direction of the ramp. 'Last one's down.'

Uriel returned his gaze to the hauler as it described a wide arc at the bottom of the ramp and the massive machine turned towards the fortress. When the cab had levelled out, but the huge trailer portion was still curved around, he rose to his feet and shouted, 'Go! Go!' over the vox and ran out into the open.

Scattered groups of slaves looked up at them as they ran for the enormous machine, but otherwise paid them no mind. Up close, the bulk-hauler was even larger than it had first appeared, fully nine metres tall and constructed of dented sheets of thick iron and bronze girders. Its wheels were solid and tore deep furrows in the ground as it rumbled onwards. Fortunately, it was still moving slowly enough to catch and Uriel leapt for the iron ladder that led to the cab above.

Space Marines jogged alongside the bulk-hauler and clambered onto the mnning boards, beginning to climb the craggy sides of the trailer. Uriel swiftly ascended the ladder towards the platform bolted to the side of the driver's cabin, hearing a heavy thump of something landing on the cab's roof. Metal tore and he heard screams.

He continued climbing, seeing the door above him burst open and a creature in a vacuum suit and leather harness emerge from the interior of the cab. Harsh, static trills of fear emitted from a copper faceplate as it saw Uriel, but he didn't give it time to react, reaching up and gripping its harness.

It tried to draw a pistol, but Uriel pulled hard and sent it spinning from the driver's cab to the ground below. Kyama Shae, the Crimson Fists Space Marine riding the running boards, shot the mutant in the head and the groups of slaves clustered around this part of the ramp cheered as it died.

Uriel scrambled up the ladder and swung into the driver's cabin, ready to fight, but saw that there would be no need. Another two creatures, clad in the same black vacuum suits as the one Uriel had thrown to the ground, lay dead in their bucket seats, torn open from neck to groin by Ardaric Vaanes's lightning claws.

The renegade sat awkwardly before a control panel, the bulk of his jump pack almost filling the cabin. He struggled with an array of levers and a giant wheel beneath a great rent in the steel roof, and said, 'Do you know how to drive this thing?'

'No,' said Uriel. 'But how hard can it be?'

'Well, we're about to find out,' said Vaanes.

Uriel wiped a hand across the blood-smeared windscreen and peered through at the rear ends of the two bulk-haulers in front of them.

'Just keep it straight, and try to stay with the two ahead for as long as you can.'

Vaanes nodded, too intent on working out the controls to the bulk-hauler to reply. Uriel left him to it and swung out onto the platform on the side of the cab.

The Space Marines of the warrior band were making their way along the running boards to the ladders at the sides and rear of the bulk-hauler, climbing up towards concealment within the empty trailer.

Satisfied they could actually get close without significant risk of discovery, Uriel clambered back into the driver's cab and dragged out the dead bodies of the mutant drivers. He hurled them from the cab, those slaves chained nearest to where the bodies fell tearing them apart with wanton abandon.

'It's not actually that difficult,' said Vaanes as Uriel closed the door behind him.

'No?'

'No, a Rhino's harder to control than this. It's just a little bigger.'

'Just a little,' agreed Uriel.

He left Vaanes to wrestle with the controls and stared through the dirty windscreen at the siegeworks beyond, the scale of the battle taking his breath away.

They passed great artillery pits, enormous guns, bigger by many times than the heaviest artillery pieces of the Imperial Guard, hurling tank-sized shells towards the fortress. Tall towers hung with bodies and spiked bunkers were spread throughout the camp and a sprawling infrastructure had arisen to support the massive effort of taking Honsou's fortress. Dark wonders and monstrous sights greeted them at every turn, the myriad horrors of a daemon world at war.

The bulk-haulers drove along corpse-hung roads, skull-paved plazas where naked madmen capered around tall idols hung with entrails and pillars of iron that crackled with powerful energy. They watched mutants hurl crippled slaves into bubbling pools of molten metal, laughing as they did so, and Uriel turned away. He could not save them all, so he would save none of them. It scarred his soul to let such atrocities go unpunished, but he was coming to believe that Vaanes was right - better to let them die than to be killed trying and failing to save them.

As the bulk-hauler swallowed up the distance between the outskirts of the camp and the siege lines, they drove over great bridges of iron that crossed deep trenches, through kilometres of razorwire and around deep pits containing screaming mechanical monsters. Shadows of great, clawed limbs swayed in the firelight and Uriel felt a shiver of dread at the thought of even laying eyes on such daemon engines.

The heat in the cab was oppressive, but he didn't dare open the door for fear of discovery. So far they had been able to continue following the bulk-haulers ahead of them, but as soon as the lead hauler turned away from the fortress, it would only be a matter of time before their ruse was discovered.

The bulk-haulers rolled onwards through the Iron Warriors' camp, driving through great shanty towns of red-garbed soldiers and blazing drumfires. Soldiers chanted in praise of their masters and fired off shots into the air as they danced around the flames.

'These are the warriors of Lord Berossus,' said Vaanes, pointing to a gold and black standard raised high at the edge of the camp.

'And who is he? A rival of Honsou's?'

'So it would seem. He is the leader of a grand company of the Iron Warriors, a vassal of Lord Toramino, one of their most powerful warlords.'

'How do you know all this?' asked Uriel.

'We have sometimes taken prisoners,' replied Vaanes, 'and did not shirk from their interrogation. If Berossus is here, then so too is Toramino. Whatever the reason they lay siege to Honsou's fortress, it must be powerful indeed.'

'Perhaps they know what Honsou brought back from Hydra Cordatus and desire a share in his spoils of victory.'

'Gene-seed? Yes, that would probably do it.'

'We can't let that happen.'

Vaanes laughed. 'We are but thirty warriors and you would have us topple this world.'