Then, as suddenly as it had begun, the faint shuddering stopped, and a moment later the surface of the sea returned to its steady chop as the Horus gently rose and dipped on the easy swell. For a moment no one on the ship moved or spoke, as if they were waiting for the strange phenomenon to begin again. Julia cleared her throat. 'Do you think it's over, whatever it was?'

'No idea,' Cato replied softly.

The brief exchange had broken the spell. Macro puffed his cheeks as he let out a deep breath and the ship's captain turned away from his passengers and scowled at the steersman. The latter had released his grip on the tiller of the great paddle at the stern of the Horus and was cowering beneath the fantail decoration overhanging the stern post. Already the ship was slowly swinging round into the wind.

'What in Hades do you think you're doing?' the captain blazed at the steersman. 'Return to your bloody post and get us back on course.'

As the steersman hurriedly took up the tiller, the captain turned round to glare at the other sailors. 'Back to work! Move yourselves.'

His men reluctantly returned to their duties as they adjusted the sail that had begun to flutter at the edges as the Horus luffed up for a moment, before the steersman leaned into the tiller and the ship settled back on to her original course.

Macro licked his lips nervously. 'Is it really over?'

Cato sensed the deck under his feet, and glanced at the sea, which looked just as it had before the tremor had begun. 'Seems to be.'

'Thank the gods.'

Julia nodded, then her eyes widened as she recalled her maid, who had been resting on her mat in the small cabin she shared with her mistress and the senator. 'I'd better check on Jesmiah. Poor girl will be terrified!

Cato released her from his arms and Julia hurried across the deck towards the narrow gangway leading down to the passengers' quarters, where those who could afford it had paid for a cabin. The rest of the passengers simply lived and slept on the deck of the Horus.

As Julia disappeared from sight, a faint cry reached them from the shore and Cato, Macro and Sempronius turned towards the land. Though the light was dim, they could clearly see figures stumbling away from the estate's slave compound. Or what was left of it. The walls had been flattened, exposing the barrack blocks inside. Only two were still standing; the rest were in ruins.

'Bloody hell.' Macro stared at the ruins. 'What could have done that?'