'An earthquake,' said Sempronius. 'Has to be. I've experienced something like it before while I was serving as a tribune in Bythinia. The earth shook, and there was a dull roar. It went on for some moments, and shook some buildings to pieces. Those inside were crushed and buried under the rubble.' He shuddered at the memory 'Hundreds died . . .'

'But if it's an earthquake, then why were we affected, out here at sea?'

'I don't know, Macro. The work of the gods is beyond the understanding of men.'

'Perhaps,' Cato remarked. 'But surely, if the tremor on land is severe enough, it would communicate itself through the water to us?'

'That may be so,' Sempronius admitted. 'In any case, we're the lucky ones. It is those on land who will have felt the full power of the gods' wrath.'

For a moment the three men stared towards the ruined slave compound, slowly slipping into the distance as the Horus sailed steadily away from the coast. A fire had broken out in the ruins, most likely from the kitchens preparing the evening meal, Cato decided. Flames licked up into the dusk, illuminating the shocked figures of the survivors. A handful were desperately picking away at the rubble to free those trapped beneath. Cato shook his head in pity.

'Be thankful we are at sea. I would not want to be ashore now. You should be grateful for that at least, Macro.'

'Really?' Macro replied quietly. 'What makes you think the gods have finished with us yet?'

'Deck there!' a voice suddenly cried from aloft. 'Captain, look!' The sailor sitting astride the spar close to the top of the mast had thrust his spare arm out, along the coast to the west.

'Make your report properly!' the captain bellowed up to him. 'What do you see?'

There was a pause before the sailor replied anxiously. 'I don't know, sir. Never seen its like. A line, like a wall, right across the sea!'

'Nonsense, man! That's impossible.'

'Sir, I swear, that's what it looks like.'

'Fool!' The captain crossed to the side of the ship, swung himself up on to the ratlines and began to clamber aloft to join the lookout. 'Now then, you bloody fool, where is this wall of yours?'

The lookout thrust his hand towards the horizon, into the fading light of the setting sun. At first the captain could see little as he squinted. Then, as his eyes adjusted to the distant gleam, he saw it. A faint glitter of reflected light rippling along the horizon, above a dark band that stretched from out to sea right up to the coast of Crete. Where it touched the land there was a churning foam of water.