‘Just be grateful you’re not standing on that other one,’ Erlan muttered back. The sight across the narrow valley was like nothing he’d ever seen. All along the high inner walls the ramparts were crowded with Byzantine troops, and amongst them tall wooden contraptions swayed and lurched as they were manhandled into position. ‘Onagers’, ‘mangonels’ – words he had learned that day, which signified the great timber monsters whose wooden arms could fling massive rocks and stones and other missiles a terrifying distance. Beneath them on the terrace between the two walls in the lee of the outer fortification awaited a sea of men in blue and red and green tunics, banners fluttering among them in the westerly wind, each flag with its many-coloured streamers marking a different tagmata – the war-bands the Byzantines divided their soldiers into. Running beyond the outer wall was a deep moat, only half-filled with water. Already it was a midden swamp of battle gear and bodies.

Beyond the moat, the approach to the city was teeming with the Arab host: foot soldiers, mounted horsemen, giant siege weapons and towers. The noise was appalling, the valley resounding with the battle-cries of the swarming troops, the distant whump of huge stone missiles smashing against the walls of the city, the thrum and shriek of flaming arrows looping in both directions.

Erlan watched one of the Arab siege engines release its mechanism. It moved differently to the stocky punch of the Byzantine onagers. Instead it unwound with deceptive grace, its long arm accelerating slowly, and at last sweeping up a pot of burning pitch and launching it like a comet through the sky. A few moments later the fireball smashed among the battlements not fifty paces south of where they stood. The boiling fire scattered among the defenders in a shower-burst of sparks and sherds of scalding clay. Their shrieks flared briefly with the flames then died away. But the walls had suffered no damage at all.

‘We should move further north, Majesty,’ advised Katāros. ‘You are too exposed here if the fighting should turn this way.’

‘Nonsense!’ Leo cried, apparently enjoying himself. ‘We’re perfectly safe. Besides, we won’t see a damned thing if we drop down the other side.’

‘We can’t afford you to suffer any harm, Majesty,’ the chamberlain insisted in his high, sober voice, just as another projectile hurtled downwards, this time exploding even closer in a cloud of white dust. ‘Quicklime,’ someone yelled. ‘Cover your mouths and eyes!’