‘I never knew this place was here.’

‘Not many do. It’s on no plans; I dare say your emirate doesn’t know it exists. When we needed a place to work in secret your mother, ever resourceful, started asking around among the criminal element.’

‘Criminal?’

‘Smugglers. Hoarders. Even bandits. They knew of this hole in the ground. It wasn’t hard to take it over, clean it up, extend it a little . . .’

‘Ah, the vizier’s advisor. How good of you to make time in your busy schedule to visit your mother.’

Ibrahim had not seen his mother for four years. Subh wore a robe, white and pristine despite the dirt, and her hair was piled elaborately on her head, jet black. Unlike Peter she showed not a trace of the passage of time; she was as upright, powerful and magnificent as ever. Peter seemed to cower before her; he was as much in her thrall as ever.

Ibrahim bent forward to embrace his Mother.

But she subtly moved back and offered her hand, cold, the palm oily. ‘Let’s keep things formal,’ she said. She showed not a trace of emotion.

‘Mother, you haven’t changed.’

‘And what of you?’ she asked. ‘You’re clean enough. A smart costume. And well fed, it seems to me.’

‘I take only my ration,’ he said stiffly, and it was true, though there were many in the palace who took more.

She prodded his belly. ‘In that case you’re not getting enough exercise.’

‘What are you doing here, Mother?’

‘You know very well. Building the war engines that might save Seville. Walk with me. See what we have made . . .’

She showed him her marvels. Here was a metal tube that used compressed steam to spit iron balls. Peter called it the ‘thunder-mouth’, for the great roar it would make when it was fired. Around the perimeter of the treadmill he had noticed was a series of crossbows. An archer sat at the axle, and as the wheel turned one bow after another was brought before him.

‘The archer only has to aim and fire,’ Peter explained. ‘See, the ingenuity is that the mechanisms of the wheel-engine load each bow for him as it turns. So this enables a much faster rate of fire than a conventional bow, without a loss of accuracy.’

There were many such gadgets, most only half-finished, betraying ingenuity but fragility.

Ibrahim refused to be impressed. ‘This is all you’ve achieved, in five years?’

Subh watched him gravely. ‘Don’t you think anything of our efforts?’

He walked around the workshop. ‘Your rapid-firing crossbow machine is vulnerable. A stick poked into the mechanism would jam it.’

Peter said, ‘But a row of these machines, fixed to the city walls when the Christians come—’