Cornelius winked at Aurelia. 'What a loss to society!'

'Be nice, Cornelius,' murmured Aurelia.

'Frankly, Thalius,' Cornelius said, 'the fate of your derivative little sect is of little interest to me compared to the use Constantine evidently plans to make of it.'

Aurelia was interested. 'And that use is?'

'Isn't it obvious? Constantine is turning the empire into a monarchy. He will be a king as supreme and unchallenged as the rulers of ancient Persia and Egypt. And he wants to draw on the unity of Christianity to cement all that in place; he imposes this alien cult on us in order to control us all.'

Aurelia said, 'You asked Thalius what he objected to in an emperor who adopted his own faith. Now I ask you, Ulpius Cornelius: what is wrong with an emperor whose goal is to unify the empire? Isn't that better than the bloody chaos of our youth?'

'Not if it is done the wrong way,' Cornelius said. 'Not if it means abandoning everything that made Rome strong in the first place. For if he does that, even if he succeeds in the short term, in the long run only ruin will ensue.'

Aurelia tutted, mocking him. 'And I had you down as a rational man, Ulpius Cornelius. Are you superstitious like Thalius here? Do you fear that if you turn your back on Rome's old gods they will punish you?'

Cornelius reddened, and Thalius saw there must be some truth in the charge. But the courtier said, 'I talk of political realities, madam. Of a system that has worked for centuries. There has always been room for another god or two in our infinitely flexible pantheon! And that way nobody, from Germany to Africa, from Britain to Asia Minor, need be excluded from the consciousness of empire. It is not its army that made Rome strong but its inclusivity.'

'But that is because Rome's gods are so like its subjects' gods,' Aurelia said. 'The Romans were farmers, as our ancestors were, Thalius. And farmers, rooted to their land, have gods of specific places. So the gods can happily coexist-each to his own scrap of land. The Jews, though, were nomads. And their god, who became Christ's God, was a god of no-place, or perhaps of all places, an infinite god of the sky. But there is only one sky, and in such a scheme there can be only one god. Now the Romans are accepting this sole nomadic god as their own. There will be a fight to the death, Cornelius, a battle between the old farmers' gods and the new sky god. There cannot be room for both. Now there will only be exclusivity, and intolerance.'

Cornelius pursed his lips, and Thalius saw his deep dislike of being analysed in this way by a provincial woman, however valid the points she made. 'Well, madam, you are here too. What is your objection to Constantine?'

Aurelia was unperturbed. Thalius imagined she dealt with bullying men like Cornelius in the course of her working life all the time. 'It's simple. My concern isn't for the fate of empires, still less for the immortal souls of humanity, but for Britain.' She railed about Constantine's excessive taxes, and repeated the rumours she had heard that Constantine had plans to move the capital of the empire permanently to the east. 'Somewhere in Greece, it is said, or Asia Minor, or even Africa. Do you know anything about this?'

The courtier pulled his lip. 'There are always rumours. And there are practical issues involved, not least the defeat of Licinius first. But, yes, there is such talk. Rome will always be the heart of the empire. But Rome isn't terribly convenient as a capital: it is far from the frontier provinces, like Britain, where the energies of the empire have to be concentrated. It is overcrowded, cluttered, difficult in the summer-'

'And,' Aurelia said laconically, 'it is full of potential opponents of the Emperor, from the ever-hungry mob to old families like yours, Cornelius.'

'I won't deny that. Here is the bald truth. The eastern provinces are far richer than the west. Isn't it sensible to place the capital at the economic core of the empire?'

Aurelia said, 'Only if you want the rest to wither away and die, neglected.'

'Well-so here we are, the Christian, the pagan and the ambitious provincial, all united in believing that something must be done. But nothing is going to happen unless we manage to decode the slave child's puzzle-tattoo-eh?'

'There is that, yes,' Thalius said gloomily.

Aurelia sighed and settled back on her couch. 'I've been working on it and have got nowhere, I'm afraid.'

Cornelius said, 'These acrostics are a Christian game, are they not? Like this one on the wall.' He pointed to a cryptogram carefully painted in a corner of the Christ portrait:

Thalius said, 'The fresco painter added it.'

Cornelius bent to see. 'Very clever. Reads the same up and down, forward and back. But so what? The sower Arepo guides the wheels carefully. What is this, some reference to a holy life? Oh, I do hate word puzzles!'

'Perhaps, but there is more in it than that,' Aurelia said. She unfolded herself from her couch, dipped a delicate fingertip in the black of an extinguished candle, knelt down by the acrostic, and with her blackened finger wrote lightly on the wall. 'Do you mind, Thalius? I am sure it will brush off. You see, you can rearrange the letters in the form of a cross, like this.'

P

A

T

E

R

O

S

T

E

R

Cornelius studied the result. 'A cross for Christ-eh? And it reads Our Father both ways.'

'The first words of the Lord's Prayer,' Thalius said.

Cornelius frowned. 'But you haven't used all the letters.' He compared the cross to the original acrostic, and dabbed his own blackened fingers to pair up the letters in each.

Thalius groaned, 'My housekeeper will disembowel me for this mess!'

Cornelius sat back. 'You made a mistake, Aurelia! You have two As and two Os left over.'

'There's no mistake,' Aurelia said. 'It's yet another layer of meaning, Cornelius, at least for a Christian. A and O, or Alpha and Omega: this symbolises the 'beginning and the end' in the Christian revelation…' Her eyes defocused. 'Oh.'

Thalius took her arm, mildly alarmed. 'Madam, are you all right?'

'No. Yes! I think I have it.'

'Have what?'

'The key to your slave's puzzle, Thalius-and perhaps the key to all our destinies.' She stood up. 'You must take me to the boy-now!'