A thud from behind caused Cato to turn back, pulling his blade free.The first guard's body had just hit the ground, the legs kicking out in a savage spasm, as the second guard ran into sight. He stopped as he made to change direction round the corner, but the sight of his two stricken comrades, and Cato looming over them, slightly crouched and ready to spring as he raised his dripping blade, was too much. He backed away frantically, back round the corner and out of sight, then Cato heard his footsteps sprinting away as the man cried out in alarm and terror.

There was no time to take any satisfaction in his small victory and Cato quickly wiped the blood from his sword on the edge of his cloak, and beckoned to Carpex.

'Take off your robe. Put on the officer's kit.'

'What?' Carpex still looked stunned in the light of the torch guttering amongst the filth on the ground.

'Put it on now,' Cato ordered harshly as he cast his robe aside and leaned over the body of the guard. He untied the chin straps and pulled the helmet and the liner off the man's head, and then undid the sword belt. Glancing round he saw that Carpex had knelt down and after a brief, reluctant pause was beginning to do the same to the rebel officer.The guard was wearing chain mail, and as ever the awkward metal rings were difficult to wriggle over the chest, shoulders and head and Cato had to wrench furiously at the mail to get it free. At once he gathered it up over his head and thrusting his arms through he let the mail slide heavily over his body. He picked up the liner and jammed it on his head before putting on the conical helmet and tying the chin straps. Carpex was still struggling to get into his mail and Cato quickly helped him. A moment later Cato picked up the torch and handed it to the slave before he bent down and retrieved the guard's spear.

'At least now we shouldn't attract too much unwanted attention. Now, get us to that tunnel, Carpex.'

The slave turned and trotted down the alley. Cato followed, sticking close to his companion so that he could see the way ahead lit by the torch. Carpex led them through the twisting network of old streets unerringly, even though it was night. Not once did they see any sign of the inhabitants and Cato guessed that they must be sheltering anxiously behind their locked doors, praying that the rebels would ignore them. At length, they entered a slightly wider thoroughfare that ended in a market square where the traders' stalls stood bare. A voice grumbled from the shadows, and as Cato and Carpex turned to the sound they saw a figure a short distance off. Before they could react the man turned and disappeared.The sound of footsteps padded away into the night.

'Must have been a beggar,' Carpex suggested softly.'They sometimes sleep in the markets. Anyway, look there, master.'

Carpex indicated a stone structure in the centre of the square with a low arched doorway.

'What is it?'

'One of the entrances to the city's sewers.The engineers use it from time to time, but it's nearly always locked.' Carpex smiled. 'At least that's what they think.'

'Locked?' Cato shook his head in frustration as they approached the heavy studded door set into the stone archway. 'What now?'

'Just watch,' said Carpex as he examined the iron bracket where the bar slid into the masonry. Drawing his dagger, Carpex scraped some of the filth away from the edges of the stones and then inserted the blade in the gap where the mortar should have been. He wriggled the blade for a moment until a square-edged piece of stone began to come out. As soon as he could grasp its edges Carpex pulled it free and placed it carefully on the ground.The bolt was exposed and now Carpex could open the locked door. The bottom grated over the flagstone and then there was a groan of protest from the hinges. Both men winced, waited a moment for a reaction, and then slid through the gap.

'How did you know about the door?' asked Cato when they were inside.

'I arranged it that way, so the prince and I could slip in and out of the sewage tunnels without anyone's knowing. If you don't look at that piece of stone carefully you'd never know it could be moved. Come on.'

Carpex ducked under the low ceiling, lighting his way with the torch held out ahead of him. Cato followed. Just inside was a small stone platform, with several stained steps leading down towards the tunnel.

'Better shut the door, master.'

Cato eased it back into its frame, keeping the noise from the hinges as quiet and gradual as possible.Then he nodded to Carpex. 'There. Now let's go.'

The steps were dry at the top, but the last few were slimy and Cato trod warily as they descended through a small arch into the tunnel. His nose wrinkled at the stench as they paused in the light of the torch.The sewer stretched out on either side as far as Cato could see by the wavering glow of the small flame. The steps disappeared into the slowly flowing current of fouled water and after a small hesitation Carpex stepped down into the flow. It came halfway up his calves as he headed to their right, in the direction of the current. With a grimace, Cato followed him. The thick atmosphere was filled with the tang of shit and piss and Cato had to swallow hard as he fought the impulse to be sick.

'How far have we got to go?'

'A few hundred paces, master. Then we're beneath the citadel.'

They had waded no more than fifty yards when both men heard a muffled squeal of iron hinges, and they paused to look back down the tunnel. The sound of voices echoed off the rough stonework and a moment later a red glow marked the low arch where the steps led up to the entrance.

'Shit,' Cato muttered. 'That beggar must have found someone.That was quick.The other guard must have alerted the whole town.'

'What do we do?'

'Could you find your way from here in the dark?'

'No.'

'Then we have to go on! Fast!'

They moved on, splashing through the filthy stream in the wildly flaring glow of Carpex's torch.Then behind them came a shout, harsh and immediate in the closed tunnel, and the churning rush of several men coming after the two fugitives.

'How much further?' Cato gasped.

'Not far. Just up ahead, a tunnel branches to the right.'

Cato glanced up and scanned the side of the tunnel.The black mouth of an opening loomed up at the limit of the orange bloom cast by the torch.

'I see it!'

They splashed up to the junction and turned into the side tunnel.

'What now?'

'Follow it for a short stretch, until there's a curve, then there's the spur going towards the old stables of the citadel.'

'Right.' Cato followed the slave as he surged on. The pursuers were lost from sight for a moment, and even the sound of their progress had diminished now that Cato and Carpex were in the new stretch of tunnel. But all too quickly the entrance behind them was illuminated by a growing glow and a moment later the rebels had followed them into the side tunnel. Just ahead Cato could see the tunnel begin to curve, as Carpex had said it would. As they splashed round the bend the pursuers were again lost from view and then Carpex pointed.

'There! See!'

A small passage opened on to the main sewer, perhaps just over half the height of the tunnel they were in. As they reached it Cato glanced in and saw that the spur sloped gently up.

'Where does it go?'

'Directly to the barracks, master. It ends just below a grille.'

'Right.' Cato took the torch from the slave and thrust him into the small opening. 'You first. Go as fast as you can. But you stop the moment we hear the rebels.'

Carpex nodded and ducked down as he scrambled up the tunnel. Cato swung the torch underarm and then lobbed it as far down the tunnel as he could. It flared through the dark air, bounced off the wall in a shower of sparks and then fell into the stinking current, hissed a moment and died, pitching the tunnel into darkness. Cato felt for the rim of the entrance to the side tunnel and bent down to ease his way into it. There was no way of walking, or even crouching, and he went down on hands and knees. There was only a trickle on the sloping floor, but it was covered with slime and small pieces of rubble. Ahead of him he could hear Carpex grunting and scrabbling up the slope. His breaths came in strained gasps and the weight of the chain mail was quickly exhausting him. They had gone perhaps thirty feet when the sounds of their pursuers reached Cato's ears.