We were given cots in an officers' tent not far from the commander's own. If Trebonius truly believed Meto to be a traitor, he was a generous man to give such hospitality to a traitor's father. More likely, he preferred to keep me close at hand so that he could be sure I left camp the next day.

Long after the others in the tent were sleeping, with Davus gently snoring nearby, I remained awake. I may have dozed once or twice, but it was hard to tell whether the images in my head were dreams or waking fantasies. I saw the canyon where we had lost our way that afternoon, the fence made of bones, the dark temple and the squat, primeval skystone of Artemis, the razed forest, the soothsayer who knew my reason for coming…

What sort of place had I come to? The next day, if Trebonius had his way, we would be off again before I had a chance to find out.

Finally I threw off my coverlet and quietly stepped out of the tent. The full moon had begun to set, casting long, black shadows. The torches that lit the pathways between tents burned low. I paced aimlessly, moving gradually uphill, until I found myself in a clearing close by Trebonius's tent. This was the crest of the hill, with a view of the city.

In the darkness, I imagined Massilia to be a great dorsal-finned behemoth that had pulled herself out of the sea and collapsed face down, then been ringed about by walls of limestone. The jagged crest along her spine was a ridge of hills. The encircling walls gleamed blue in the moonlight. Impenetrable shadows lurked in the bends of the towers. Torches, mere dots of orange flame, flickered at regular intervals along the battlements. On either side of the city, outside her walls, two bays opened into the sea beyond; the larger inlet on the left was the main harbor. The still face of the water was black, except where moonlight burnished it silver. The islands beyond the city, behind which Caesar's ships lay moored, were lumpy gray silhouettes.

Between the high place where I stood and the nearest stretch of wall lay a valley lost in shadows. Across the gulf of air, that stretch of wall seemed disconcertingly close; I could clearly see two Massilian sentries patrolling the battlements, torchlight causing their helmets to flicker. Behind them reared a dark hill, the crested head of my imagined sea monster.

Somewhere in the darkness encircled by those moonlit walls my son had died, swallowed up in the belly of that recumbent behemoth. Or else he still lived, pursuing a fate as shadowy as the night.

I heard footsteps and sensed a presence behind me. A sentry, I thought, come to send me back to my bed; but when I turned I saw that the man wore a sleeping tunic. He was quite short and had a neatly trimmed beard.

He stepped up to a spot on the crest of the hill not far off, crossed arms, and studied the view. "Can't sleep either?" he remarked, not really looking at me.

"No."

"Neither can I. Too excited about tomorrow."

"Tomorrow?"

He turned his head, studied me for a moment, then frowned. "Do I know you?"

"I'm a visitor from Rome. Arrived earlier tonight."

"Ah. I thought you were one of Trebonius's officers. My mistake."

I studied him in return. I smiled. "But I know you."

"Do you?" He peered at me. "It's the darkness. I can't-"

"We met at Brundisium a few months ago, in circumstances not dissimilar to this. Caesar was laying siege. Pompey was trapped in the city, desperate to sail away. Caesar was building extraordinary earthworks and breakwaters at the mouth of the harbor, trying to close it off and trap Pompey's ships inside. You pointed out the structures and explained the strategy to me, Engineer Vitruvius."

He clicked his teeth, furrowed his brow, then opened his eyes wide. "Of course! You arrived with Marc Antony, just before all Hades broke loose." He nodded. "Gordianus, isn't it? Yes, I remember. And you're-you're that fellow Meto's father."

"Yes."

There was a silence, uncomfortable on my part. Together we stared at the moonlit view.

"What do you know about my son?" I finally asked.

He shrugged. "Never had occasion to meet him. As an engineer, I've always dealt with others among Caesar's officers. Know him by sight, of course. Seen him riding alongside the imperator, taking notes while Caesar dictates. That's his function, I understand, assisting Caesar with letters and memoirs."

"What else do you know about Meto? There must be rumors." He snorted. "I never listen to camp gossip. I'm an engineer and a builder. I believe in what I can see and measure. You can't build bridges by hearsay."

I nodded thoughtfully.

"Is he in camp, then-your son?" asked Vitruvius. "Come to visit him, have you, all the way from Rome? But then, you traveled all the way from Rome to Brundisium to see him there, didn't you? The gods must have given you a harder backside for traveling than I've got!"

I kept my face a blank. Vitruvius didn't know, then. The tale of Meto's betrayal was confined to those higher up or closer to Caesar's immediate circle. I took a deep breath. "Trebonius tells me there's no way into Massilia," I said, casually dropping the siege commander's name.

The engineer raised an eyebrow. "It's a well-fortified city. The walls extend all the way around, one continuous circuit along the land, along the sea, and also along the sandy beach that fronts the harbor. The walls are made of massive limestone blocks, strengthened at intervals by bastion towers. Extremely well constructed; the blocks appear to be perfectly fitted and stacked, without cement or metal clamps. The lower courses have slits for shooting arrows. The upper battlements have platforms for machine-bows and torsion artillery. This isn't like laying siege to some Gaulish fort thrown together with logs, I can tell you that! We'll never ram our way in, never bring down the wall with catapults."

"But the walls can be breached, nonetheless?"

Vitruvius smiled. "How much do you know about laying sieges, Gordianus? That son of yours must have learned a thing or two campaigning with Caesar up north and editing his memoirs."

"My son and I usually talk of other things when we meet." He nodded. "I'll tell you about sieges then. The main virtues of the besieger are patience and perseverance. If you can't crash or burn your way in, you must burrow like a termite. The sappers will have all the glory in this siege. They're the ones who dig, burrowing under the walls. Burrow far enough, and you've got a tunnel into the city. Burrow deep and wide enough, and a section of wall comes crashing down under its own weight."

"It sounds almost too simple."

"Far from it! It takes as much thoughtful engineering and hard labor to bring down a city as it does to build one. Take our situation here. Caesar chose this spot for a camp because it's high up. Not only can you see the city and the sea beyond, but you have a clear view of the siegeworks going on in the valley just below us. That's where the real action is. Right now it's too dark, the valley's all in shadow, but come dawn you'll be able to see what we've accomplished down there.

"The first step in any siege is to dig a contravallation-that's a deep trench parallel to the city walls protected by screens. That allows you to run men and equipment back and forth. Our contravallation runs all along that valley down there, from the harbor to our left, all the way over to the smaller inlet to our right, on the other side of the city. The contravallation also protects the camp from the city; prevents the enemy from pouring out of the gates and mounting a counterassault against us. At the same time, it hinders anyone beyond the camp from running fresh supplies into the city. That's important. Hunger is every man's weakness." He ticked his fingers, reciting a list. "Isolation, deprivation, desperation, starvation: no battering-ram can match the power of those.