His eyes touched mine with skepticism. "A forty-year-old pot, in military service? It's a bit of a stretch, don't you think?"

"It might have been broken years earlier," I argued, "by somebody else."

"Oh, right. I'm sure the wild Caledonians, when they weren't busy painting themselves blue and attacking people, served all their meals in Samian ware."

Refusing to concede the point, I changed the subject. "Howard also said that Dr. Lazenby was looking for me."

Adrian always had been quick at putting two and two together. Swinging round, he raised an eyebrow. "Not to offer you a place on the Alexandria dig?"

"Apparently, yes..."

"Right. That's you gone, then, isn't it?"

"I don't know."

"Verity." Adrian's tone was superior. "This is me, remember? I know quite well what the merest mention of the word 'Alexandria' can do to you."

"Yes, well, I haven't actually spoken to Lazenby, yet," I defended my indecision. "And there isn't any rush—he doesn't leave until September."

Adrian smiled briefly before swinging his gaze back to the monitor. "D'you know, if I'd known you were going to get this attached to Quinnell, I'd have left you down in London."

"Hindsight," I reminded him, "is everything. Anyway, it's too late. If I wasn't committed to Peter before, I certainly am after talking to Howard."

"Why? What else did Howard say?"

"Only that Peter Quinnell was a flaming crackpot who oughtn't to be counted among the ranks of real archaeologists."

Adrian slanted a patient look sideways at me. "Well, darling . .."

"Oh, it isn't what he said, Adrian, as much as how he said it. You should have heard him, he was so bloody patronizing. It needled me, a bit," I confessed.

"And?"

"What do you mean, 'and'?"

“If I know you, you'd not let Howard get away with being patronizing."

In response to his obvious amusement, I lifted my chin a fraction and let an edge of defiance cut into my own voice. "Well, as a matter of fact, I bet him a fiver we'd find a marching camp of the right period."

"That's my girl. Blind faith was always your best quality."

"It's not blind faith, it's—"

He cut me off. "Bloody hell," he said, without violence. He was staring at the screen of his computer, and something in his expression made me sit up smartly, instantly alert.

"What is it?"

"Look at this." He moved aside to make room as I rolled my chair closer and peered at the jagged black-and-white bands. At first glance, the radar profile bore a striking similarity to the image he and Fabia had faked, the boundary ditch and rampart marked at nearly the same spot by a sharp dip in the lines. But Adrian was pointing to a different, smaller feature. "There, do you see that?"

"What is it?"

"Hang on a minute." A few clicks on the computer keyboard replaced the single image with six smaller ones, while Adrian explained. "I made several runs across that area, this afternoon, and this is what the chart recorder printed off. You see? There's one blip, there. And that's another."

I scrutinized the profiles. "I count three."

"Right. Now," he told me, keying in another series of commands, "let me show you what they'd look like, on our site map."

The image on the screen changed shape again, becoming a topographical map section of the southwest comer, on which the three mysterious blips now showed as small black dots.

I shook my head. "They could be anything."

Ignoring me, Adrian drew in the known line of ditch and rampart, and positioned one more dot on the screen. "Look again," he advised.

I looked. He was speculating, of course—adding the fourth dot to create a perfect square, set at an angle to the rampart's corner curve. Still, the image was suggestive. On any other site, I would have said those dots were post holes, hinting at some buried structure underneath the level turf. And on any other site, I'd have been tempted to identify that structure as a guard tower, only ... only ...

"I'm afraid you've lost your fiver, darling," Adrian said slowly. He sounded nearly as stunned as I felt, and he turned his head to lock his eyes with mine. "This is no marching camp."

THIRD HORSE

And hear at times a sentinel

Who moves about from place to place,

And whispers to the worlds of space,

In the deep night, that all is well.

Tennyson, "In Memoriam", CXXV

XVI

Quinnell rejected the evidence. "Your equipment must be off, my boy," he told Adrian, leaning forward to tap the computer screen with an accusing finger. "Blips on the landscape, that's all. Or the remnants of a garden shed."

It was obvious to me why Peter didn't think that what we'd found could be a guard tower. Roman marching camps didn't have any permanent structures—only forts and fortresses had guard towers.

And our site could not have been either.

Roman forts were much too small. Built to defend and supply the spreading imperial forces, they were occupied by auxiliary troops, not legionaries. The famous fort at Housesteads on Hadrian's Wall could have barely held a quarter of a legion, and that only if the men stood cheek to jowl.

At the other end of the scale, a legionary fortress would have been enormous—fifty acres or more. And we knew from our surveys and excavations that our ditch and rampart had enclosed an area of roughly twenty acres. Which left us somewhere in between—too large to be a fort, too small to be a fortress. Marching-camp size, as a matter of fact.