The figure put a finger to his lips then gestured for them to follow. In single file, Calgacus, then Demetrius, Maximus bringing up the rear, they set off.
At first they went to the right. They were sheltered there, between the wall and the gentle pitch of the roof. Demetrius walked carefully, one hand on the wall, watching where he put his feet, afraid a tile would shift or give way.
They turned left into a ridged dip where the roofs of two houses came together. At the end was another drop, a bit deeper this time. One by one, they turned round, lay down flat, pushed their legs out, wriggled backwards, hung by their hands for a second and let go. The landing site was the apex of a roof.
The figure indicated they were again to go to the right. Demetrius felt his heart shrink. The pitch of this roof was steeper, and it ran down to the black, square opening of an atrium. Slip here, and there was nothing to stop you sliding all the way down, over the edge and out into emptiness; a fall of two storeys to a shattering impact on a concrete impluvium. Demetrius imagined his smashed body lying there, his blood staining black the waters of the shallow raintank.
Their mysterious guide climbed down, fingers hooked into the gutter at the top, legs spread wide, and edged crabwise along the horrible slope. Calgacus followed. Demetrius stared at the gutter. It looked so fragile: his existence would hang by an insubstantial piece of fired clay.
'No choice, boy,' Maximus whispered in his ear. 'Don't look down.'
Fumbling, clumsy with fear, Demetrius lowered himself. He could feel the heat of the day's sun still in the tiles under his body. Tentatively, he began to edge along. Athene, Artemis, all the gods hold your hands over me. Inch by inch he crept. Great Zeus, Hermes, protector of travellers. His palms were slick with sweat. He crept further. Fear sent little spasms of cramp running through his limbs. His breath was coming fast and shallow. He looked over his shoulder. The tiles went on and on, sickeningly steep, dropping into yawning black nothingness. His muscles locked. He could not move.
Demetrius felt Maximus grip his right wrist, Calgacus his left. The mere touch of the other men made the young Greek feel a little calmer.
'We will guide you,' Calgacus said in his ear. 'One hand at a time. Mine first.'
Demetrius felt the increased pressure on his left wrist. Reluctantly but obediently, he unclenched his fingers and let Calgacus move his hand along. He grasped the next length of guttering. Maximus repeated the procedure with the other hand.
Only once did Demetrius look to his left. The roof stretched away into the distance. A wave of panic rose in him. He fought it down. He kept his eyes on the tiles under his nose. Hand by hand, Maximus and Calgacus helped him along.
Demetrius became aware that Calgacus was shifting his position. A moment later, his boot struck the roof that extended out to form the next side of the atrium. A jerky scramble and the Greek boy was on the ridge, legs either side, in no danger of a fall for the time being.
On the far side of the ridge, a gentler slope ran down to a low wall. They slithered down. Past this was a drop to a stepped lane. No matter, they were safe where they were. In the shelter of the wall, they paused to get their breath back. Somewhere, not far away, a baby was crying. It had not struck Demetrius that the noise they were making could wake those sleeping in the houses below. At any moment, they might raise the alarm. Suddenly, he was eager to be moving again.
Calgacus touched Demetrius's arm. They were off once more, crouching below the level of the parapet wall, using their hands, scurrying like monkeys. This uncomfortable but unthreatening way of moving lasted all too short a time. The wall on the right and the roof on the left were at an end. Demetrius was unhappy to see Calgacus get down on all fours. The Caledonian crawled out on to a free-standing wall.
Great Athene of the Aegis, I can do this, thought Demetrius. On one side, there was a drop to the stepped street, on the other an equally awful fall to a paved courtyard. I can do this. Grey-eyed Athene, I can.
Demetrius inched out. The top of the wall was a couple of feet across. No reason to fall. Just keep going. No earthly reason to fall.
He was concentrating so hard on keeping his balance that he almost bumped into Calgacus. The Caledonian had stopped and was manoeuvring himself to lie down full length. Not knowing why, Demetrius did the same.
The noise came from behind. The Greek boy peered anxiously over his right shoulder and down. Two watchmen were walking down the street. They carried lanterns, and each had a club over his shoulder. As they drew nearer, Demetrius could hear one of them talking.
'So the tribune says, "So, Centurion, is that how the men use the camel?" And the centurion says, "No, Tribune, they use it to ride to the nearest brothel."'
The other watchman laughed briefly. 'That joke was old when Cronos was young,' he said. When he was level with Demetrius, he stopped. He held up his lantern and shone it into a small courtyard on the other side of the street. He went in and carefully looked all around a fountain in the middle. Gods below, he was far too diligent.
The watchmen moved on. The humourist started up again. 'Do you know the one about the donkey and the murderess?'
'Yes,' replied the other unencouragingly.
Giving the impression that such rebuffs were not uncommon, his companion stopped and put his lantern down on a step. He retied his laces. Retrieving the lantern, he stood up and walked on. Then, without warning, he stopped again. He turned to look back the way they had come. Then he looked up.
'Thieves! There up on the wall!'
Calgacus was up, running fast. Without time for thought, Demetrius was doing the same.
The slope of the roof loomed in front. Scrambling up it, boots slipping on the tiles, Demetrius glanced down. The first watchman had a bell in his hand. Demetrius saw him pull out the straw which held the clapper in place. Its clanging echoed across the sleeping city.
Their unintroduced guide led the fugitives on. The pitch of the roofs here was gentle. Up and down they went, vaulting over ridges. Fear gave wings to Demetrius's feet. Below, the watchmen were chasing. Somewhere in front, another bell was ringing.
'Alley ahead. No problem to jump.' In the stress, the guide's eastern accent had dropped away.
Demetrius saw Calgacus leap the divide. Demetrius found himself mouthing one of Ballista's sayings – Do not think, just act.
As soon as he took off, the young Greek knew he had mistimed it. Arms flailing, he was dropping too fast. His stomach thumped into the edge of the roof, knocking the wind out of him. He was slipping back. His fingers clasped the corner of a tile. It came loose. He was slipping faster, legs thrashing in the void. Far below, the tile shattered.
Demetrius clung to the final row of tiles. They began to shift. A hand gripped his wrist. Calgacus's face was contorted with effort; Demetrius's weight was dragging the old Caledonian with him.
'Let go,' Demetrius screamed.
Slowly sliding to his doom, Calgacus hung on. Sweat was pouring down his ugly old face.
Another hand grasped Demetrius's other wrist.
'One, two, three, pull!' Together, the guide and Calgacus managed to haul Demetrius up a little.
'One, two, three, pull!' Demetrius's chest was over the lip of the roof. He clawed himself fully over. His saviours yanked him further up. Calgacus was doubled up, holding his injured arm. Maximus landed like a cat behind them.
'This way, quick!' The guide was off again.
Below, the streets and alleys echoed with shouts and the ringing of bells. Here and there shutters were thrown back, light spilling out.