They moved before dawn on the third day.
Five hundred riders arranged in three working layers, stretched across a front broader than a force this size should have occupied.
The lead scouts were already a full day ahead. Twelve men, moving in pairs, carrying light gear and simple orders to map, observe and avoid engagement.
The middle screen consisted of forty riders spread across a two-mile band. Wide enough to cover terrain, tight enough that mirror flashes or fire signals could pass between them within minutes.
The main column rode behind them, Batu beside Torghul near the center.
The rear observation screen was the part Batu had designed most carefully.
Twenty riders divided into four groups, each responsible for a quarter of the rear arc.
Their task was simple. Watch whatever followed.
The first day passed cleanly.
The steppe opened westward in long flat swells. Grass bent under constant wind. Cloud cover kept the sky gray, the temperature low, and visibility clear.
Good conditions. The horses stayed fresh. The pace held steady.
Batu spent most of the day studying how reports moved through the formation.
A rider in the middle screen spotted a herd of wild horses to the northwest and sent a mirror signal rearward.
The message reached Torghul in eleven minutes.
Torghul classified it as a false contact and signaled to continue without slowing the column.
The formation absorbed the report and kept moving.
Eleven minutes was too slow.
In an actual engagement, eleven minutes separated choosing ground from reacting too late.
But it was the first day, the men were still learning the system's rhythm. Batu stored the number and withheld comment.
That evening they camped on a low rise with open sight in every direction.
Batu ate with Torghul and two middle-screen commanders. He asked each man the same question.
What had you seen but not reported, and why.
Two of the three answered immediately.
Minor observations, terrain irregularities. A cluster of old fire pits suggesting a seasonal camp. A patch of churned ground that could have been livestock or riders traveling in column.
Neither officer had reported the details because neither had been sure they mattered.
"Report everything."
Batu ordered. "Your job is only to observe, not to decide any significance."
They accepted the command. He continued.
The problem arrived on the second day, midmorning.
The northwest rear observation group sent a mirror signal toward the main column.
Batu caught it before Torghul's signal officer did because he'd been monitoring the rear arc himself.
Riders in the north.
He counted the flashes to confirm.
Thirty to forty riders, matching the formation pace, holding distance.
"Ulus outriders," Torghul said, reading the same signal.
"The headman sent word east," Batu said.
He'd considered that possibility from the beginning. He hadn't expected such a clean confirmation on the second day.
"I want twenty riders pulled from the rear line for a wide northern sweep, two miles out. Set a pace that brings them even with the Ulus force in roughly an hour. Keep weapons sheathed and ride easy. Let them see our riders."
Torghul studied him.
"Show them we know they're there."
"Show them we knew before they believed we knew."
Torghul dispatched the riders.
Batu monitored rear-arc signal traffic for the next ninety minutes while the main formation continued at a measured pace.
The flanking detachment curved north.
The Ulus outriders maintained movement for forty minutes. Then the rear screen reported a change.
Slowing.
Stopping.
Turning northward in a direction that carried them away from the column's route.
The formation never altered stride.
Two hours later the twenty riders returned to the rear line.
Their commander, a compact young officer named Chaidu, gave his report. The Ulus group had been watching from a ridge when Chaidu's riders rose into full view.
The Ulus force had counted the riders, looked south toward the main column, measured the risk, and decided to be somewhere else.
Good.
The message had moved north without anyone speaking.
A clan that had ridden out to observe had withdrawn without any probe skirmish.
That report would reach the Ulus headman before nightfall.
Numbers alone would not have communicated about the force advancing toward Tergesh territory.
But while Batu's attention had been tied to the Ulus situation, the middle screen had been operating without complete oversight.
And during the second hour of the Ulus contact, while both Batu and Torghul were focused north, one pair from the middle screen dropped out of the signal pattern.
The signal officer noticed first.
He reported it to Torghul without urgency. A missed signal had many ordinary explanations.
A lame horse. A rider delayed by terrain inspection. A mirror lost in shifting cloud shadow.
Batu heard the report and noticed the particular atmosphere of the silence that followed.
One pair missing. Two riders.
Responsible for a quarter-mile segment on the left flank of the middle screen.
Two hours without contact.
That left-flank section was also the closest part of the screen to the direction from which the Ulus riders had appeared.
"How long before we know whether this is a problem?" Batu asked.
"If they miss the next check, I'll send a rider to their last position," the signal officer said.
"Send one now."
The rider left.
Twenty-five minutes later he returned with both missing scouts riding behind him.
Uninjured.
One horse had thrown a horseshoe crossing a rocky section and gone lame. The rider had focused on controlling the animal and missed two signal checks before his partner realized the problem and covered it manually.
A thrown horseshoe.
Two hours of blindness on the left flank.
Batu studied the two men.
They were competent soldiers that thought the failure came from equipment rather than incompetence. Not entirely their fault. Not acceptable either.
"If those thirty Ulus riders had been two hundred," Batu said coldly, "and if they'd been moving toward our flank instead, what would two hours of silence in that section have cost us?"
Neither man answered.
They understood.
Batu continued. "Every scout carry a spare and the tools to set it. If a horse goes lame, your partner signals and holds position while you make the repair. The screen contact does not break for any reason short of enemy attack."
He turned his horse toward the formation.
Behind him, the two scouts exchanged a look. He didn't need to see it to know it happened.
Embarrassment taught quickly.
He rode forward to where Torghul waited.
"The Ulus issue is contained for now," Batu informed him.
"And the screen?" Torghul asked.
"It failed once. In a place where failure could have been expensive."
He looked west toward the flat horizon. The Tergesh camp lay somewhere beyond it, roughly a day's ride away.
"It'll fail differently next time. The job is to refine it until it is foolproof."
Torghul was silent for a moment. "You expected failure."
"I expected something to go wrong. I didn't know where."
Batu kept his eyes on the horizon.
"That's the purpose of a test."
They made camp an hour before dark.
The fires rose in patterns, visible from distance, arranged to imply a force larger than five hundred.
Another small adjustment. Another careful placement.
The Tergesh headman was one day away.
He'd seen the Ulus riders withdraw north.
Somewhere in his camp, he was building a picture from fragments. Batu had built that picture carefully, meant to unsettle without announcing its purpose.
Tomorrow would be the real test.
Whether polite defiance still held when confronted by hundreds of riders standing at its door.