The Russian writer had not mentioned a gate, which meant that either it had been added after his trip through the tunnel, or she was in a different passageway. She felt the bars of the gate again. They had been spaced to keep out men in armour, but she might be able to fit through. She pushed her head through first, and then, turning sideways and holding her breath tight, she just managed to squeeze through. She continued down the tunnel into the darkness. She could hear a new sound now, a deep, repeated booming, which sounded to her like the heartbeat of the earth. It took her a moment to realize what it was: cannons. Eventually, the sound faded away. She could only guess what that meant. Had she passed them? Was she moving away from some exit that she had missed in the dark? Despite her doubts, she kept walking. A weak light began to fill the tunnel, and in the distance she spied a pile of large stones blocking the way ahead.
Sofia hurried forward. It looked as if there had once been a small room here, with stairs leading upwards — just as the Russian had described the exit from the tunnel. She dropped to her knees and moved among the fallen rocks, looking for a way through. Finally, she found it: a narrow passageway that wormed its way up through the rubble to where she saw a thin sliver of blue sky. She wriggled into the passageway, but after several feet, her progress was blocked by a large stone. Sofia shoved against it, and the stone shifted slightly. She braced her legs against the sides of the passage and pushed harder. This time, the stone rolled aside, revealing the blue sky beyond.
Sofia pulled herself upwards until her head poked out of the tunnel. She was on the side of a small hill, hidden by tall grass. The heavy, flat stone that had covered the tunnel entrance lay to the side. She looked about, but saw nobody. She wriggled the rest of the way out of the hole and crouched in the grass. Before her, empty hills rolled away into the distance. To her right was the final stretch of the Golden Horn. She turned around and edged her way up the hill. When she reached the top, she dropped to her stomach in the grass. Only a hundred yards in front of her lay the Turkish encampment, stretching away far into the distance, all the way to the walls of Constantinople. As the sun reached its zenith overhead Longo walked the walls alongside Dalmata, inspecting the damage wrought by the Turkish cannons. They started at the Blachernae wall, just north of the palace. This was the newest section of the wall, built in the seventh century to enclose the Blachernae quarter. Unlike the rest of the land wall, it was only a single wall, but it was thick and had held up well to the bombardment.
'The walls are stronger than I had imagined,' Longo said.
'Wait until you see the Mesoteichion,' Dalmata told him. 'It is where they have placed their largest cannons.'
They continued and crossed over on to the innermost of the Theodosian walls, built over one thousand years ago, in the early days of the Eastern Roman Empire. At first, the walls looked strong, but as they sloped down towards the Lycus river, gaps began to appear in the outer wall. By the time they reached the Mesoteichion — the area around where the Lycus river passed through the walls — the gaps had become the norm, and stretches of wall the exception. The inner wall was still more or less whole, but the outer wall had been almost completely destroyed. Longo stopped and looked down on the ramshackle stockade that had been built on the rubble. Dirt had been thrown on the debris to create a walkway, and then planks and sacks of earth used to create a low barrier. At the top, barrels filled with dirt formed a battlement, providing the defenders with some cover.
'The stockade cannot hold up to their cannons,' Dalmata said. 'The soldiers draw lots to see who will defend it each day, and who will rebuild it each night.'
Dalmata's words were punctuated by a tremendous boom. A moment later, the stockade below them exploded in a shower of dirt and splintered wood. As the dust settled, Longo saw that a gap five feet wide had been blown in it. In the middle of the gap, an enormous cannonball sat buried amidst the wreckage.
Longo shook his head. 'What was that?'
Dalmata pointed to where a huge cannon sat on the Turkish rampart some two hundred yards away. 'The men call it the Big Bastard,' he said. 'The Turks call it the Dragon. Either way, it's a monster. Nothing we build will stand up to it.'
A palace messenger approached them along the wall. 'Signor Giustiniani, I bring a message from the Princess Sofia,' the man said. He handed Longo a folded note. It read: I have important information. It is urgent that I speak with you. Come to the palace, quickly. — Princess Sofia.
'I must go,' Longo told Dalmata. 'We can continue this later.' Longo hurried to the palace, where Sofia's maidservant guided him to the library. Longo found Sofia standing at a table examining a large map. 'Princess Sofia,' he said and bowed.
Sofia looked up from the map. 'Come, look at this,' she told him. Longo moved to stand beside her. She smelled of honeysuckle, and as she leaned forward over the map, she revealed the soft curves of her cleavage. Longo forced himself to look away to the ancient map spread out before him. It was a plan of subterranean Constantinople, detailing cisterns, sewers and underground tunnels. 'This is part of a series of surveys from the twelfth century,' she said. 'Do you see this underground chamber, where the many tunnels come together?'
'What of it?' Longo asked. The chamber in question looked to be near the wall. Tunnels radiated out from it towards the palace and to other parts of the city.
'The map is incomplete,' Sofia said. 'Look at the edge of the chamber here, where these lines are indented. Do you see the smudging? A tunnel has been erased.'
'Are you sure?' Longo asked.
Sofia smiled. 'I found the tunnel myself this morning. It leads out past the walls and beyond the Turkish army. The entrance to the tunnel is beneath this palace.'
'Have you told anyone of this? The emperor? Notaras?'
Sofia shook her head. 'No. Secrets are not easily kept in this city. If our enemies find out about these tunnels, then we are lost.'
Longo looked back to the map. 'You are right. If the Turks make their way into these tunnels, then they will have access to the entire city.' He looked up from the map, and their eyes met. 'But why tell me and not the emperor?'
Sofia lowered her eyes. 'You are in command of the city's defences,' she said, and then looked back at Longo. 'And I trust you.'
Longo stared into her hazel eyes. 'I will not disappoint you,' he told her. From the doorway the maidservant coughed, and Longo straightened and looked back to the map. 'I will have my men destroy the tunnel. Is it the only one that leads under the walls?'
'It is the only one that I have found,' Sofia said. 'There could be others.'
'Let us hope not. In the meantime, I need to see this tunnel as soon as possible. Can you take me to it?'
'Not now,' Sofia replied, lowering her voice. 'We would draw unwanted attention to the tunnels and ourselves. I do not wish to fuel idle gossip. Meet me at midnight, outside my quarters, and make sure you are not seen.' Longo consulted with Constantine until late that night. He suspected that more than information on how the siege was progressing, the emperor simply wanted company. He did not blame Constantine. The emperor was battling to prevent the end of an empire that had lasted more than a thousand years.