'The boy has the eyes of a preying bird,' Maximus said, resting his hand on my head and gazing down into my face. He should know; his own eyes had something of the predator as well. 'I do not believe I have ever seen eyes of such colour in a man before – like yellow gold.' His smile was dagger sharp. 'Tell me, Merlinus, what do you see with those golden eyes of yours?'

An odd question to ask a child of seven. But an image formed itself in my mind:

A sword – not the short, broad gladius of the legionary, but the long, tapering length of singing lightning of the Celt. The hilt was handsome bronze wrapped in braided silver with a great amethyst of imperial purple in the pommel. The jewel was engraved with the Eagle of the Legion, fierce and proud, catching sunlight in its dark heart and smouldering with a deep and steady fire.

'I see a sword,' I said. 'The hilt is silver and bears a purple gem carved like an eagle. It is an emperor's sword.'

Both Maximus and Lord Elphin – my father's father, who stood beside me – looked on me with wonder, as though I had spoken a prophecy great and terrible in its mystery. I merely told them what I saw.

Magnus Maximus, Commander of the Legions of Britain, gazed thoughtfully at me. 'What else do you see, lad?'

I closed my eyes. 'I see a ring of kings; they are standing like stones in a stone circle. A woman kneels in their midst, and she holds the Sword of Britain in her hands. She is speaking, but no one hears her. No one listens. I see the blade rusting and forgotten.'

Although Romans were always keen for an omen, I do not think he expected such an answer from me. He stared for a moment; I felt his fingers go slack in my hair, and then he turned away abruptly. 'King Elphin! You look fit as ever. This soft land has not softened you, I see.' He and my grandfather walked off, arms linked: two old friends met and recognized as equals.

We were there at Caer Cam the morning he arrived. I was training the pony Elphin had given me, desperate to break the wily creature to the halter so that I could ride it home in a few days' time. The little black-and-white animal seemed more goat than horse and what had begun as a simple trial with a braided rope harness soon grew to an all-out war of wills with mine suffering the worst of it.

The sun was lowering and the evening mist rising in the valley. Wood pigeons were winging to their nests, and swallows swooped and dived through the still, light-filled air. Then I heard it – a sound to make me stop rock still and listen: a rhythmic drumming in the earth, a deep, resonant rumble rolling over the land.

Cuall, my grandfather's battlechief, was watching me and became concerned. 'What is it, Myrddin Bach? What is wrong?' Myrddin Bach, he called me: Little Hawk.

I did not answer, but turned my face towards the east and, dropping the braided length of leather, ran to the ramparts, calling as I ran, 'Hurry! Hurry! He is coming!'

If I had been asked who was coming, I could not have made an answer. But the instant I peered between the sharpened stakes I knew that someone very important would soon arrive, for in the distance, as we looked down along the valley, we could see the long, snaking double line of a column of men moving northwest. The rumble I had heard was the booming cadence of their marching drums and the steady plod of their feet on the old hard track.

I looked and saw the failing sunlight bright on their shields and on the eagle standards going before them. Dust trailed into the dusky sky at the rear of the column where the supply wagons came trundling on. There must have been a thousand men or more moving in those two long lines. Cuall took one look and sent one of the warband racing for Lord Elphin.

'It is Macsen,' confirmed Elphin, when he arrived.

'Thought as much,' replied Cuall cryptically.

'It has been a long time,' said my grandfather. 'We must make ready to welcome him.'

'You think he will turn aside?'

'Of course. It will soon be~dark and he will need a place to sleep. I will send an escort to bring him.'

'I will see to it, lord,' offered Cuall, and he strode away across the caer. Grandfather and I returned to the survey of the valley road.

'Is he a king?' I asked, though I knew he must be for I had never known anyone to travel with such an enormous warband.

'A king? No, Myrddin Bach, he is Dux Bntanniarum and answers only to Imperator Gratian himself.'

I searched my scant Latin… dux… 'Duke'?

'Like a battlechief,' Elphin explained, 'but far greater; he commands all Roman forces in the Island of the Mighty. Some say he will be Imperator himself one day, although from what I have seen of emperors a dux with a cohort at his back wields more power where it counts.'

Not long after Cuall and ten of Elphin's warband rode out, a party of about thirty men returned. The strangers were strange indeed to my eyes: big, thick-limbed men in hardened leather or metal breastplates, carrying short bulky swords and ugly iron-tipped javelins, their legs wrapped in red wool which was tied to mid-thigh by the straps of their heavy hob-nailed sandals.

The riders pounded up the twisting path to the gates of the caer and I ran round the ramparts to meet them. The timber gates swung open and the iron-shod horses galloped into the caer. Between two standard bearers rode Maximus, his handsome red cloak stained and dusty, his sun-darkened face brown as walnut, a short fringe of a black beard on his chin.

He reined the horse to a halt and dismounted as Elphin came to greet him. They embraced like friends long absent from one another, and I realized that my grandfather was a man of some renown. Seeing him next to the powerful stranger my heart soared. He was no longer my grandfather but a king in his own right.

As other horsemen entered the caer Elphin turned to me and beckoned me to him. I stood at stiff attention while the Duke of Britain inspected me closely, his sharp, black eyes probing as spearpoints. 'Hail, Merlinus,' he said in a voice husky with fatigue and road dust, 'I greet you in the name of our Mother, Rome.'

Then Maximus took my hand in his, and when he withdrew it I saw a gold victory coin shining there.

That was my first introduction to Magnus Maximus, Dux Britanniarum. And it was before him then and there that I spoke my first prophecy.

There was feasting that night. After all, it is not every day that the Duke of Britain visits. The drinking horns circled the hall, and I was dizzy trying to keep them filled. Through a timber hall dark with the smoke of roasting meat and loud with the chatter of warriors and soldiers regaling one another with lies of their exploits on the twin fields of bed and battle, I wandered, a jar of mead in my hands to refill the empty horns, cups, and bowls. I thought myself most fortunate to be included in a warrior's feast – even if only as a serving boy.

Later, when the torches and tallow lamps burned low, Hafgan, Chief Bard to my grandfather, brought out his harp and told the tale of the Three Disastrous Plagues. This brought forth great gales of laughter. And I laughed with the rest, happy to be included with the men on this auspicious night, and not sent down to the boys' house with the others.

What a night! Rich and raucous and full, and I understood that to be a king with a great hall filled with fearless companions was the finest thing a man could achieve, and I vowed that one day this fine thing would be mine.

I did not speak to Maximus again while he stayed with Lord Elphin, though he and my grandfather talked at length the next day before the Duke departed and returned to his troops waiting in the valley. I say I did not speak to him, but when his horse was brought to him and he swung up into the saddle, Maximus saw me and raised his hand slowly, touching the back of his hand to his forehead. It is a sign of honour and respect – an unusual gesture with which to favour a child. No one else saw it, nor were they meant to.