Water was an incompressible fluid with a thickness of sixty-two point four pounds per cubic foot.
When fifty thousand gallons of it dropped two hundred upright feet through a smooth, friction-minimized concrete channel, it ceased to be a liquid and became a liquid battering ram weighing over two hundred tons.
On the snow-swept northern plateau, two hundred and fifty screaming brigands charged across the white wasteland at a dead sprint.
At their head rode Warlord Bronn, his black destrier kicking up clouds of frozen turf, his two-handed greatsword blazing with greasy potion-made fire.
The raiders carried scaling ladders, iron grappling hooks, and wood-cutting axes, their minds driven into a frenzy of suicidal fury.
They reached the edge of the frozen moat.
The ice sheet looked white, clean, and solid under the gray morning sky.
“Onward,” Bronn roared, plunging his warhorse down the snowbank onto the glistening surface. “Ride them down. Scale the stones.”
Behind him, two hundred and fifty armored men swarmed onto the ice, their boots pounding in an ear-splitting stampede.
Up on the high southern aqueduct bridge pillar, thirty feet above the battlefield, Giles Croft stood beside the massive four-foot bronze emergency water gate wheel.
Beside him, Master Borin Bronze-Lung held a six-foot iron cheater pipe slipped over the wheel spokes to provide extra leverage.
Before opening the water gate, Giles had checked the solid strength of the energy fading away basin at the foot of the spillway chute.
“Check the baffle blocks, Duncan,” Giles called out, leaning over the stone railing. “A fifty-thousand-gallon discharge carries huge moving scour potential. If that torrent hits an unprotected earth ditch, it scours thirty feet of foundation silt and undermines Pier Forty.”
“Ten concrete chute blocks anchored to the bedrock with two-inch iron dowels,” Duncan replied. He nodded with grim satisfaction. “Cast from our densest fiery volcanic cement mix. Each tooth weighs four tons. When the torrent hits those baffle teeth, it forces a high-pressure jump, killing sixty percent of the forward speed.”
“A classic Froude number high-pressure jump,” Giles murmured, noting the flow shift on his slate. “The striking force converts to churning eddy fading away inside the stilling pool, leaving a broad, subcritical wave front that flushes the surface without eroding the stonework scarp.”
“Target hostiles fully committed to the drainage basin,” Giles said, reading the posture through his brass pocket sextant. “The entire leftover assault echelon is situated within the main scour channel.”
He placed his hand on the cold bronze rim.
“Turn the wheel, Borin. Open the drain tube gate.”
Borin threw his entire dwarven weight against the iron cheater bar.
CLACK-CLANK.
The heavy hard dark metal-bronze gate valve, holding back two miles of high-pressure mountain water, lifted eighteen inches from its machined seat.
For one second, there was only a low, underground hiss like escaping steam.
Then, from the dark belly of the concrete channel inside the cliff face, an earth-shaking, thunderous roar erupted.
It sounded as if a mountain was splitting in half.
ROOOOOOOOAR.
At the northern aqueduct spillway. There, the high stone arch ended above the moat, a huge wall of emerald mountain water burst from the tunnel mouth.
It didn’t trickle down the stone scarp. It exploded horizontally at forty-five feet per second under eighty-six pounds of pressure of high-pressure head pressure.
A twelve-foot-high tidal wave of foaming, crystal-clear mountain water surged into the frozen moat.
The impact of two hundred tons of moving liquid striking four inches of static ice was a world-ending cataclysm.
The frozen ice sheet didn’t merely crack.
It blew up.
Thousands of square feet of white ice shattered into millions of jagged slabs and blocks, churned into a frothing, churning whirlpool of roaring white water.
The high-pressure surge tore through the twenty-foot-wide ditch like a freight train of liquid granite.
The wave struck the advancing bandit host at the midway point.
Men screamed in terror as the solid ground beneath their feet ceased to exist in an instant.
The twelve-foot wall of roaring water and churning ice boulders slammed into two hundred and fifty armored men with the force of an avalanche.
Warhorses, scaling ladders, iron shields, and screaming brigands were swept into the air like dry autumn leaves.
Bronn’s black destrier was knocked off its hooves by a three-ton block of floating ice. It rolled sideways into the surging flood.
The warlord’s flaming greatsword was ripped from his gauntlet by the roaring torrent, its potion-made fire hissing into greasy steam before vanishing into the depths.
Men clad in forty pounds of ringmail had no power to swim, fight, or resist.
The raging water seized them, rolling them over and over through churning ice slush, carrying them down the natural slope of the moat ditch.
The water didn’t drown them against the walls. Giles’s carefully graded high-pressure slope channeled the entire surge northward into the broad, shallow gravel flats of the river gorge.
Ladders splintered against boulders. Axes and broadswords were torn from hands and buried beneath three feet of washed river silt.
The entire army was flushed out of the moat like autumn leaves swept from a rain gutter.
Up on the castle walls, Master Duncan Stone-Splitter dropped his stonemason’s hammer. He gripped the low roof wall with both hands as he laughed until tears rolled down his cheeks.
“Look at them go,” Duncan laughed, his voice booming over the receding thunder of the water. “They wanted to cross our moat. The moat just washed them all the way to the sea.”
Sister Teresa stood atop the gatehouse platform, her hands lifted to the stormy heavens as she gazed upon the receding floodwaters.
Her eyes shone with thrilled, triumphant awe.
“The sky river has burst forth,” Teresa called out, her voice ringing across the valley like a church bell. “As Pharaoh’s chariots were drowned in the Red Sea, so hath the Living Stone swept the wicked into the wilderness. The mountain has spoken.”
Giles wiped water droplets from the brass casing of his pocket watch, resetting the stopwatch second hand with a sharp click.
“It’s not a sky river, Teresa,” Giles said patiently. “It’s an unthrottled high-pressure drain tube discharge governed by Torricelli’s law of efflux speed. The fluid simply followed the minimum energy high-pressure grade line down to the river basin.”
Teresa turned to him with a radiant, blissful smile that entirely bypassed his physics lecture.
“Torricelli or the Sovereign, Lord Giles. The wicked are disarmed, the water is pure. Our walls stand without a single stone displaced.”
Giles closed his pocket watch, giving up on the holy debate.
Along the upper gravel embankment, Sister Teresa and Mistress Pippa had established three massive cast-iron soup cooking pots over open charcoal trenches.
The cooking pots bubbled with rich, steaming beef broth infused with dried parsnips, crushed barley, and healing cloves.
Four novice healers moved between the shivering lines of captured raiders, distributing steaming wooden bowls of broth and thick wool horse blankets.
“Drink it slowly,” Teresa instructed a shivering youth who was weeping into his bowl. “Let the salt and ginger restore the heat to your chest. The Sovereign grants you life this day. Spill not the soup.”
Mistress Pippa refilled an empty ladle from the boiling kettle. Her round face was flushed with heat.
“Thirty bushels of winter barley and ten kegs of pickled beef expended,” Pippa noted cheerfully to Lady Millicent. “A small price to pay to turn two hundred freezing cutthroats into peaceful canal diggers.”
Down in the gateway courtyard, Captain Kenneth Drake drew his broadsword and raised his iron-shod pacing rod.
“Form rescue squads,” Kenneth ordered eighty assembled guard post constables and quarrymen. “Ropes, blankets, and stretchers to the gravel bars. Round up every man on the flats before they freeze.”
The heavy outer oak gates were thrown wide.
Kenneth led sixty disciplined guards down the wet, steaming raised stone road.
The scene on the wide gravel banks three hundred yards downriver was one of total, total capitulation.
The roaring floodwaters had crested. That left the shallow gravel bars littered with two hundred and twenty gasping, shivering, half-drowned brigands.
Their weapons, armor, and siege gear had been washed into the deep river rapids or buried under tons of fresh gravel.
Men lay on the stones in their sodden tunics, coughing up river water, weeping with freezing misery, their hands raised in total, total surrender.
Not a single man reached for a weapon. Not a single man tried to run.
They were soaked to the bone in sub-zero air, their teeth chattering wildly, utterly broken in spirit by a castle that fought with rivers instead of steel.
Kenneth’s constables moved step by step through the shallows, tossing woolen blankets over shivering shoulders, binding wrists with soft hemp twine, and lining the prisoners up in disciplined columns of four.
Giles walked out across the steaming raised stone road, with Toby Karr and Lady Millicent.
He paused at the edge of the scarp. He looked down at the gravel flats where forty men lay motionless or groaned weakly.
Giles felt that same cold, heavy knot tighten in his chest.
Thirty men had succumbed to freezing shock or trauma against the rocks during the flash flood.
Kenneth was grinning, treating the capture of two hundred and twenty prisoners as a masterstroke of bloodless warfare. But Giles stopped beside a drenched, unmoving form on the gravel.
He knelt down, checking the man’s neck for a pulse.
Cold. Still.
Giles gently pulled the dead man’s sodden wool cloak over his face. He stood up with a quiet, somber expression.
“Every operation has an inescapable human casualty margin,” Giles murmured to Toby. “Never celebrate a casualty count, Toby. A dead hostile pawn produces zero economic return and leaves an unfillable ledger deficit.”
Toby looked down at the fallen raider, the boy’s cheerful smile fading into quiet, sober maturity. “Yes, Lord Giles. I understand.”
Millicent dipped her quill into her ink-horn, recording the final figures with quiet respect.
“Two hundred and twenty living prisoners secured,” Millicent said softly. “Fed, housed, and put to work in the quarry, their labor will rebuild everything their warlord sought to destroy. That’s the true victory of Grey Crag.”
A sudden, furious splashing sound echoed from the riverbank fifty yards away.
Giles, Kenneth, and Millicent turned their heads toward the water’s edge.
Out of the freezing river rapids crawled a huge, monstrous figure.
Warlord Bronn.
The warlord’s black armor was dented and coated in gray river mud. His horned helmet was gone, revealing a bald scalp covered in jagged battle scars.
He coughed up a mouthful of gravel and blood. He dragged himself onto the snowbank with feral, unbending hatred.
In his right hand, he clutched a shattered three-foot fragment of his blackened greatsword, its steel edge chipped and smoking faintly with dead potion-made ash.
He saw Giles Croft standing on the high raised stone road above him.
Bronn’s bloodshot eyes widened with insane, murderous fury.
He dragged himself to his feet, swaying like an angry bear, his chest heaving as he pointed the broken blade straight at Giles’s heart.
“Master builder,” Bronn roared, his voice cracking into a ragged, bloody shriek. “I’ll cut your heart out of your ribs.”
The warlord lunged up the frozen gravel ramp toward the raised stone road, charging with the last dying ember of his berserk strength.