Grace shrugged. ‘The seventh King Henry isn’t long on his throne. These brothers haven’t toiled for centuries to put bombards in the hands of one pretender to the English crown or another.’

Ferron nodded. ‘We have a higher purpose than the ambitions of kings, we are waging a war which transcends all others. You have chosen the right course - you and your forebears, for centuries.’ He had recovered his composure, James noticed, amused.

Now they were walking among the engines. They passed wheeled platforms, and huge hulls like steel houses, and blunt cannons whose mouths gaped, and more exotic forms yet, complicated masses of machinery with no clear purpose. On one bench lay a huge skeletal wing, twice the length of a man’s body. There was a stink of oil and hot metal, the air was dense with steam, and the labouring monks, wide-eyed in the gloom, scurried out of their way.

James said, ‘It might seem simple to translate given designs into actuality. In fact much of our work is at a more basic level, as we learn to make the components required by our engines. Steel hard enough to make screws and gears that will not shear was a particular challenge. Advanced cannons need just the right casting, loading, lighting and cooling if we are to increase their capacities and speed of fire.’

Ferron confessed, ‘I understand little of what I am seeing.’

‘The engineering detail doesn’t matter,’ Grace said. ‘Our purpose is only to show you the scope of the work here. The practical demonstration aboveground later will show you all you need to know.’

Ferron smiled thinly. ‘A demonstration? I’ll look forward to it. And all of this comes from the fevered brow of this Roger Bacon?’

‘He worked from the designs and recipes in the Codex of Aethelmaer, returned from its hiding place in Seville . . .’

Bacon had quickly abandoned his Aristotelian studies and had thrown himself into experimental, secretive research. He had recruited students and assistants, and had discreetly sounded out like-minded savants across Europe. He appointed a Picard called Peter de Maricourt as his domum experimentorum, and it was de Maricourt who had set out the design for the first laboratory-manufactory.

The work progressed quickly. But as he aged, Bacon himself became more difficult. He had always been a man who craved attention and recognition. He campaigned for the acquisition of more experimental knowledge about the natural world, and began to compile a vast encyclopaedia of all the known sciences. But he made plenty of enemies by expressing his strong contempt for those who did not share his passions, and he was severely disciplined by superiors who thought he was out of control. Bacon, ever grandiose, appealed over their heads, even direct to Pope Clement. The death of Clement ended his ambitions, and his career.