"Oh, all right," Ferdulf said sulkily, and hopped up into the air. What happened next made everyone who saw it exclaim in surprise and alarm. As Ferdulf rose, so did the wall in front of him.

He exclaimed, too-angrily. He didn't much care about obeying Gerin. Having the Elabonian Empire thwart him was something else again. But as fast as he flew, as high as he flew, whichever way from side to side he flew, the wall rose to keep him from passing over it. When he flew lower, it shrank, as if it, or the wizard in charge of it, could sense exactly how high he was at any given moment.

When he returned to the ground, the wall went back to being what it had been before he started flying: ten feet high, and very solid-looking. Gerin rubbed his nose. It felt as solid as it looked.

"You ought to knock it down," Ferdulf said. "A wall like that has no business existing in the first place."

"Van didn't have much luck. And if it's magical, I'm not sure we can knock it down," Gerin said. "For instance, how thick is it?"

"I don't know," Ferdulf answered. "I think you're pretty thick yourself, though, if you stand here and let it baffle you."

Rihwin the Fox came riding over to Gerin. "Nice piece of work, isn't it?" he said with the tones of one admiring a fellow professional's achievement even when that achievement inconvenienced him. He'd studied sorcery down in the City of Elabon till a jape played on a senior wizard got him expelled from the Sorcerers' Collegium. Despite that expulsion, he'd been a better mage than Gerin up to the moment when Mavrix took away his sorcerous powers. He still knew magic well, even if he couldn't work it any more.

"I'd like it better if it weren't so nice," Gerin said.

"Oh, but it's as pretty a use of the law of similarity as I've ever seen," Rihwin protested, "not only in building the wall, but also in making detection of the keystone-or rather, in this case, the key brick-as difficult as possible."

"What nonsense is he spouting now?" Aragis demanded irritably.

Gerin took no notice of his fellow king. "Father Dyaus," he whispered. "I do believe you're right."

"Of course I'm right," Rihwin said. "When have you ever known me to be mistaken, pray tell?"

"Only when you open your mouth," Gerin replied, which reduced Rihwin to irate splutters. Gerin ignored those, too. He walked up to the wall and examined it brick by brick. Sure enough, each brick was identical to all its neighbors: not just similar to them, but identical. Each one had a chip near the center, each had a scratch at the upper left-hand corner, and each, over to the right, had embedded in it a tiny crystal or flake of mica that sparkled when the light caught it at the right angle. "Isn't that interesting?" he murmured.

"Now you're the one full of drivel," Aragis complained. "Tell me at once what's going on."

"One of their wizards took a brick and sorcerously duplicated it about as many times as there are drops of water in the Niffet," Gerin answered. "If I could find out which brick is the real one, I wouldn't have any trouble-well, not much trouble-making the wall disappear."

"Ah," Aragis said, and then, "All right. I was beginning to wonder whether you were able to talk sense or not. I see you are. Good. As I told you, I wanted you on my side because of the wizardry you know. Now-find that brick and get rid of it."

Rihwin had the grace to give Gerin a sympathetic look. "It's not quite so easy as that, I'm afraid," Gerin said. "One of these bricks along the bottom row is sure to be the brick, but which one? Go ahead, lord king-you tell me which one it is."

"You're the wizard," Aragis said. "You're the one who's supposed to know things like that. Now get to work, curse it." He might have been ordering a lazy serf to spread manure over a field.

"I can't tell which brick it is by looking, any more than you can," Gerin said. "That means I've got a couple of thousand to choose from. And that's liable to mean we'll be here for a while."

"Can we go around the bloody thing?" Aragis asked.

"Maybe," Gerin said, "but I wouldn't bet anything I cared to lose on it. My guess is that, if the wall can go up and down to keep Ferdulf from flying over it, it'll go from side to side to keep us from getting by it."

"That makes more sense than I wish it did," Aragis said. "How do you go about finding out which brick is the brick, then?"

"You have not put forward an easy question, lord king," Rihwin the Fox said. "The essence of the law of similarity centering on resemblance, distinguishing between prototype and likeness is by its nature a daunting task."

"If it were easy, the cursed imperials wouldn't have bothered running up the wall in the first place," Aragis retorted. He folded his arms across his chest and looked over toward Gerin. "Well?"

"Well, my fellow king, much as I hate to disappoint you-and to disappoint myself, I might add-I haven't the faintest idea which one is the brick," Gerin answered. "I told you that once already. Maybe I can figure out some sort of sorcerous test, though the gods only know how long that'll take or whether it'll work. You'd need a god to tell you which one brick out of thousands is the real one and…" His voice trailed away. "You'd need a god-or maybe a demigod. How about it, Ferdulf?"

"You want something more from me?" Ferdulf said indignantly. His sigh declared that he was put upon far beyond anything his powers might have made acceptable. "There are times when I wonder why the gods ever bothered creating mortals in the first place."

"Some Sithonian philosophers wonder whether mortals didn't create gods instead of the other way round," Gerin said, which made Ferdulf, despite being descended from a Sithonian deity, give him a horrible look. He wished he'd kept his mouth shut. Since he hadn't, he went on in smoothly ingratiating tones: "Be that as it may, can you use your own great powers to see what we cannot? It would give you another chance to have a go at the Elabonian Empire, and embarrass the imperial wizard who put up the wall thinking it would stop us so easily."

"Oh, all right." Even in agreement, Ferdulf was petulant. In that, he took after his father. He floated up a foot or so into the air and drifted along to the west a couple of hundred yards. "It's this one right here." He didn't raise his voice-or Gerin didn't think he did-but it came as clear as if he'd been standing by the Fox. A helpful soldier ran forward and set his hand on the brick after Ferdulf left it.

Gerin trotted over to it, ignoring the weight of his bronze-and-leather armor. To look at, it was just another brick in the wall. He'd expected nothing different. He turned to Van, who'd followed him. "Will you do the honors?"

"I will, and gladly," the outlander answered. He smashed at the brick with the bronze-headed hammer. When a chip flew from it, chips flew from all the others along the wall. Soldiers cheered. Van hit the brick again and again, till it cracked in three places. The rest of the bricks cracked, too. Van pushed at one of the pieces with his foot. It came away from the rest of the brick-and the wall vanished.

About a hundred feet behind it stood a fellow in a fancy robe who looked absurdly surprised to be staring all at once at the entire army of the northlands. "That's a wizard!" Gerin exclaimed as the man turned to run. "Don't let him get away."

"I'll take care of that," Van growled. He snatched up a piece of the brick he had broken and flung it at the sorcerer. It caught him between the shoulderblades. He went down on his face with a dismayed squawk. Before he could get to his feet again, Dagref and a couple of other men who'd run after him jumped on him and frogmarched him back to Gerin and Aragis.

"Hello," the Fox said mildly. "I gather you're to blame for this latest bit of unpleasantness?" The wizard didn't answer. Gerin clicked his tongue between his teeth in mock dismay. "And I remembered manners south of the High Kirs being so much smoother than they are here in the northlands. Tell us what to call you, anyhow."