The project had taken quite a while to complete, even by the standards of the Adeptus Mechanicus (which considered taking only one century to construct a battleship a dangerous matter of haste). Three consecutive civilisations, only one of them human, had risen and fallen in the worlds of the small star cluster since construction began.
In two cases, the fall of the civilisation had been due to efficient kinetic bombardment to break up the species' home worlds for raw material. In one case the civilisation had not so much fallen as been conquered by the off-duty security of the construction site and recruited into the workforce. Fortunately that had been the human civilisation - the overseer had seen more foolish mistakes over his many many years of duty.
Raw materials hurled across interstellar voids at near-luminal velocities arrived almost daily to be intercepted and their trajectories altered to slow them into stable orbits after several close orbits of the construction site's secondary star. Those close passes tended to result in quite a bit of the early smelting before mining vessels the size of moons moved in to strip the surfaces. They could then be left to cool in the interstellar night for a few centuries before the miners returned to take the new surface, peeling away layer after layer until nothing was left.
The habitats that had once housed the workforce were now gone. They had long since been recycled for their raw materials - admittedly materials making up less than one-thousandth of a percent of the ship but that was one-thousandth of a percent that needed less than half as much effort to prepare it for use. Now the workers dwelt upon what they were making, occuying great sprawling cities inside the continent-sized decks of hundreds of various sub-sectors. Several had been misplaced and one had been accidentally vented into space three thousand years ago.
There was still some minor finishing work to do - in fact, it was likely that interior work would continue for at least a thousand years to come. Somewhat longer than embarkation of the crew complement was to take in fact. Still, the crew themselves would handle much of it, in between the centennial maintenance schedule (currently expected to take one hundred and five standard years, but practise would no doubt improve efficiency).
It was time to begin fuelling. The first load of fuel was already aboard of course - to all practical purposes the ship was built around it. In the control chambers of the engineering section, Engineering Titans went to work, harnessing the output of the construction site's primary star - now housed in one of the ten thousand fuel bins which ancient Mechanicus lore described as Dyson Spheres.
Fuelling was expected to take thirty to forty years and would of course leave the star cluster with no stars. That was acceptable. Every planet, asteroid and comet in the cluster had long since been used up, so they were serving no other useful purpose.
The overseer was quietly proud of his achievement. Not so much for bringing it to this point thirty-seven years ahead of schedule or for completing the largest feat of engineering in the Galaxy since the fall of the Old Ones, as for the fact that this would leave the entire Eldar race entirely in the shade. Comorragh indeed!
There was an outraged roar as the ship, encased in the largest Gellar field since the Emperor's first experiments with the Golden Throne (no one had actually needed Proxima Centauri, or so he hoped) battered its way into the Warp. Billions of daemons that had been innocently going about their business in this part of the immaterium were run down without mercy by emblems of the Imperial Faith as large as Khorne's very throne.
The handful lucky enough to avoid direct contact could only watch the the mighty vessel's progress, seeing the proud name of Imperium One blazoned upon the stern and below it, in slightly smaller script the ship's motto.
'We Brake For No One But Him'