‘Perfectly!’ Apollodorus smiled confidently. He stepped forward and slapped one of the buttress timbers. ‘It will take a hundred men pulling on the ropes to dislodge each of these. When the time comes, that is exactly what will happen, once we’ve cleared the route that the flow will take down to the tributary leading into the Tiber. For now, nothing short of an earthquake will shift these. Once the water behind this dam has drained, we’ll move up the vale, draining each pool in turn until we reach the lake. That way we can control the flow of water and there’ll be only the slightest of rises in the level of the Tiber for a short time.’ He stood back and looked up at the dam with undisguised pride in his achievement. Then, conscious of the Emperor once again, Apollodorus turned to him hurriedly. ‘The celebration to mark the completion of the project is ready, sire. Just round the bend in the vale there, on the bank of the river. If you would do me the honour?’

‘What? Oh, yes. Yes, of course!’ Claudius smiled. ‘It would be m-m-my pleasure, young man. Lead the way!’

Narcissus stepped forward. ‘Sire, it is late in the day. It is already unlikely that we will return to the city by nightfall. It would be wise to set off for Rome without delay.’

‘Nonsense!’ Claudius frowned. ‘What? Are you afraid of the dark? In any c-case, this man has done a wonderful j-jo-job. The least we can do is celebrate his success.’

Narcissus bowed his head. ‘As you wish, sire.’

The Emperor patted Apollodorus on the back. ‘Lead on, my boy! L-lead on!’

The vale curved gently to the right before giving out on to an expanse of open ground. Two hundred paces beyond, the river gleamed in the sunshine as it flowed towards Rome. Several tables had been arranged together and covered with an expanse of red cloth. On the table sat a huge cake, artfully constructed to resemble the dam they had just seen. Thirty or forty of Apollodorus’s staff stood waiting beyond the table and bowed their heads at the Emperor’s approach.

Claudius smiled in delight as he reached the table and inspected the cake. ‘Excellent! Most excellent! I trust it tastes as good as it looks?’

‘It should, sire. The best cooks scoured Rome for ingredients to prepare it.’

‘This looks delicious. I’ll be the first to taste it, if I may?’

‘Of course, sire.’ Apollonius clicked his fingers and a slave ran forward with a spoon for the Emperor. Claudius paused a moment and then dipped it into the blue jelly behind the dam and turned to his retinue. ‘Tribune Burrus. One of your men please.’ Claudius turned to the engineer. ‘I m-me-mean no offence, but I have to be sure.’

‘I understand, sire.’