With a roar the volunteers chopped at the ropes before them. The banners fell away, billowing, some trailing from stray threads. The sunlight struck the Wall, struck shining surfaces exposed for the first time in centuries – tremendous concave mirrors – and was thrown back at the advancing mob, in tight, precise splashes that glared brilliantly from the white of the ice. Those caught in the light threw up their hands to shield their eyes, and cried out in pain. Steam rose from the melting ice, itself brightly lit.

Crimm, dazzled, tried to see. ‘Some are fallen, burned. A lot more are running from the light. Scared out of their wits!’

Ayto shook his head. ‘Never believed this old gear would work.’

‘Those Greeks were clever. It’s said they used mirrors to fry enemy ships in battle.’

‘Yes, but I’ve been to Greece, and the mothers know the sun is a lot stronger down there than it is here. But still, I bow to the scholars. Has it made any difference to the battle, though? I mean it’s not as if we can aim this thing. We can only fry those who kindly wander into the hot spots.’

‘Yes. Others are coming on.’

‘We’ve a fight before us yet.’ Ayto drew his sword from its scabbard, an unfamiliar weapon for a fisherman despite their hasty citizens’ training by the guard.

Now more voices started calling up and down the face of the Wall. ‘Be ready! Here they come!’

Crimm leaned over the rail again. He saw that advance parties of the invaders had reached the tumbled rubble at the base of the Wall. It took them more effort to clamber over the heaped, ice-slippery stuff, and the hungry fighters were already exhausted. And they were greeted by chunks of rubble, frost-smashed thousand-year-old growstone thrown from the balconies higher up and the roof of the Wall, and a sparse hail of arrows.

Yet they came on. Now the leaders were clambering up the face of the Wall itself. Slick with ice it might be, but the ancient growstone was so rough and frost-damaged that it offered plenty of handholds. Crimm saw a man climbing up directly towards him, knife in mouth, arms and legs bare, ruined boots on his feet, so thin he looked like an animated skeleton. Yet he climbed with purpose and strength. His eyes met Crimm’s.

The Annid of Annids was right beside Crimm, looking down as he was. He took her arm. ‘Please, Ywa – get back into shelter. It’s not safe.’

She shook him off. ‘I must be seen, in the Armour of Raka. I must be seen!’

Ayto hefted his sword. ‘Forget about her. Be ready—’

There was a yell from above. ‘Look out!’

Crimm twisted and looked up. Heavy stone blocks were hailing down from the roof, meant for the invader, bouncing down the face of the Wall. Ayto grabbed him and pulled him back.