Walking back up the tunnel with Julius and Avidus behind him, Scaurus asked the question he knew Petronius was eager to answer.
‘So Prefect, just how are they going to get past the men Narsai’s general will have set to watch the river?’
He could practically see the smug smile on the other man’s face.
‘It’s a simple question of expectations, Legatus. One of the secrets of a successful siege defence, or so I’ve come to believe, is to persuade the enemy to trust their own expectations of any situation where doing so might give us an advantage. This is the moment when we show them that at least one of those expectations is not well founded.’
The boat was moving more swiftly now, drifting silently with
the Mygdonius’s flow as the waters that rose far to the north in the mountains rushed southward, their noisy burble disguising the occasional slap of water against the Night Witch’s side. The river curved briefly to the west, hugging the walls, then turned south again, and Marcus’s view steadied as the boat master eased the boat through the bend without so much as a ripple to betray its presence before steering for the western bank. The vessel’s bow kissed the rough earth for long enough that the crew were able to lean out and wield spikes, driving the iron deep into the soft earth where land and water met, then pulling on them to drag the craft into the shadow of the river’s lip. Looking down the shimmering line of water to the south, Marcus realised with dismay that there were indeed watch fires burning to either side of the river, at the point where the Parthian siege lines ran down to the water.
‘How are we going to get past those sentries?’
Thracius spat over the side, looking over the Roman’s shoulder at the waiting sentries and considering the question before answering in a hoarse whisper.
‘By means of a right nasty shock, Tribune.’
He looked back at the fortress with a grimace.
‘When the prefect gives the order, there’s going to be a few of them Parthian bastards wishing they’d not sat quite so close to the fire.’
The three senior officers emerged into the torch-lit street, Petronius leading them to a doorway that opened onto a spiral stair, climbing vigorously up towards the top of the city walls.
‘Ever since your legion marched in here with that motley collection of soldiers at your heels, the Parthians have been busy digging siege trenches, and of course we’ve been equally busy trying to disrupt them.’
Emerging from the stairs onto the walls’ broad fighting platform, he strolled across the flat stones to the nearest of the city’s bolt throwers, larger versions of the legion’s Scorpions, deadly engines of wood, metal and sinew. The weapon and its crew were lit from behind by a pair of torches whose flames guttered and spat in the gentle breeze.
‘This beauty can hurl one of these …’
He took a bolt from the leader of the weapon’s crew and handed it to Scaurus, an evil iron-tipped length of dense, hard wood with metal flights pinned to its tail to provide stability in the air.
‘What’s the slot for?’
Petronius glanced down at the bolt’s metal nose, and the long rectangular hole that had been drilled through the iron spike. He took the missile back and passed it to the crew’s leader, a keen-eyed chosen man.
‘Demonstrate to the centurion how our night shooting works, would you?’
Deft fingers threaded a folded length of cloth through the slot, the material hanging out on either side.
‘We soak the cloth into lamp oil, First Spear. Then we put a light to it, so that when we loose the bolt you can see it fly all the way to the target, which lets us adjust our aim just as long as we can see something to shoot at.’
The prefect patted the man on the shoulder.
‘We’ll get out of your way. Things are going to get busy very shortly.’
He led them away to stand by the parapet, looking out over the sea of camp fires that marked the Parthians army’s closest approach to the fortress walls.
‘You see gentlemen, we’ve been shooting the occasional bolt at them over the last few days, but the bastards have been delighted to see that we could only land the blasted things within twenty or thirty paces of their lines. Seems that some bright lad noted our initial shots and used them to set the siege line at a safe distance. We got lucky the other day and bounced a bolt off a piece of rock, and some poor unsuspecting soldier walking through their camp stopped it between his shoulders, but apart from that all we’ve done is waste good iron …’
He paused, grinning conspiratorially.
‘That, and convinced them they’re out of range of course. Which, as you might have guessed, isn’t strictly true, not given that all those shots were taken with the springs only wound back to three-quarters of their full torsion. If, however, we wind them back until they’re creaking …’
He turned to his first spear.
‘I think it’s time to provide our messengers with a little distraction. Shall we begin?’
The senior centurion saluted and turned away, raising his voice to a stentorian below.
‘All bolt throwers – load!’
The crews leapt into action as the order was repeated by their officers in a chorus of equally loud roars, the command rippling round the city walls as each crew in turn leapt to their task, their swift and precise response to the order testimony to long hours of drill. Loaders laboured to wind back their weapons’ thick strings with straining muscles while the crew commanders waited, cloth-tipped bolts in hand. Watching the nearest machine, Scaurus smiled quietly as the chosen man gingerly fitted the missile to the waiting machine’s taut bowstring.
‘Ready!’
A chorus of similar shouts rang out as the crews stepped away from their labour, each commander taking a burning taper and standing ready to light the waiting missile’s incendiary cargo while the last fine adjustments were made to the weapon’s point of aim.
‘Shoot!’
The tapers dipped in unison to set light to the waiting bolts, and then, with a whip crack of unleashed power, the weapons spat their deadly missiles out over the space between city and besieging army, the bolts’ flaming path describing a gentle arc down towards the unsuspecting Parthian siege line.
‘Reload!’
The air above the waiting boat’s crew was suddenly alive with screaming missiles, a dozen fiery streaks shrieking down into the Parthian lines to impact with audible thuds. Somewhere in the darkness a man was suddenly screaming, pausing only to draw breath before howling more helpless outrage at whatever it was that had happened to him. The sound stopped suddenly, silenced by a merciful sword stroke, Marcus surmised, and the sound of voices raised in fear and anger reached their ears.
After a short wait another volley of bolts whistled into the Parthian line, their aim adjusted to concentrate on the only available points of aim, given the lack of either moon or stars to illuminate the battlefield. More than one shot hit the target at which it had been aimed, sending showers of sparks and chunks of burning wood flying as the heavy bolts smashed into the enemy watch fires. Half a dozen missiles landed around the watch posts on either bank of the river, at least one finding a human target to judge by the wet, crackling sound of impact, and the chorus of imprecations and shouts from the hapless Parthians redoubled. A commanding voice was raised over the furore, bellowing a single repeated command. The boat master laughed, calling to his crew.
‘Hah! He shouts to extinguish the fires! Cast off, but use your oars to back water and keep us from drifting. We must be ready, but the time is not yet.’