Late autumn, 1354. The Palazzo Venezia, Rome.
Julian sat in a high-backed chair upholstered in crimson velvet, staring blankly at the parchment unrolled across the ebony table.
Standing beside him, an elderly man in the crimson robes of a Cardinal pinched the bridge of his nose, letting out a sigh.
"Your Highness," Cardinal Orsini said, his voice dripping with a mix of pity and exhaustion. "I understand your hesitation. To go from the Fourth Prince of the Holy Roman Empire to... well, this... is a difficult pill to swallow. But if you do not sign the investiture for the Barony of Grimwall, the Emperor your father will have no choice but to send you to the monastery in the Alps."
Julian blinked, pulling himself out of a vivid, terrifying hallucination.
"Sorry," Julian said, his voice raspy. "I was just... thinking about the view."
Only three weeks ago, Julian had been Commander Elias Thorne, NASA astronaut, on his third tour of the Lunar Gateway. He remembered the catastrophic seal failure in Sector 4.
He remembered looking out the viewport as his oxygen saturation dropped below critical levels.
And then, he had woken up in a four-poster bed in Rome, screaming about hull integrity, only to be slapped in the face by a wet nurse named Martha.
He had died looking at the stars, only to be dragged back down into the mud of the 14th century.
"The monastery might be warmer," a sneering voice cut through the room.
Julian shifted his gaze. Leaning against a marble column, swirling a goblet of wine, was a young man with a face similar to Julian's, though twisted into a permanent expression of arrogance. Prince Louis, his older brother.
"Don't be cruel, Louis," the Cardinal chided gently, though he didn't look up from the documents. "Prince Julian is merely... processing the reality of his station."
"He's stalling because he knows Grimwall is a death sentence," Louis laughed, taking a sip of wine. "It's a bog, Julian. A festering sore on the edge of the Empire. The peasants there eat bark, the bandits run the roads, and the last Baron died of a fever that turned his skin black. It's fitting, really. The useless Prince gets the useless land."
Julian looked down at the map again. He was stalling because he was trying to read the archaic Latin cartography.
He traced the borders of the Barony of Grimwall with a finger. It was tiny. A speck on the map of Europe, wedged between a dense forest and a jagged mountain range, dominated by a massive river delta that the map labeled Palus Inutilis.
Hellish start, Julian thought. He ran the numbers in his head. As a fourth son with no military backing and a reputation for drinking and poetry, he was a loose end. Loose ends in the Middle Ages usually met the sharp end of a dagger or a cup of poisoned wine.
Exile to a "useless" Barony was actually the safest option. If he could survive the starvation, the disease, and the bandits, that is.
"Cardinal," Julian said, his voice steady. "This river... the Serpentine. It flows through the center of the territory?"
Cardinal Orsini looked surprised that Julian was even looking at the geography. "Yes, Your Highness. It is the source of the flooding that renders the land unarable. It is a curse."
"And the elevation here," Julian pointed to the northern ridge. "This is limestone?"
"I... I believe so. Why does it matter?"
"It matters," Julian murmured.
He looked at the map with the eyes of an engineer who had spent a lifetime studying fluid dynamics and structural integrity in zero-gravity environments.
To the medieval eye, Grimwall was a swamp. To Julian, it was a hydraulic goldmine. The drop in elevation from the mountains to the delta was significant. The "swamp" was only a swamp because the natural drainage was blocked by silt accumulation at the bottleneck near the southern border. If he dredged that bottleneck and built a series of simple sluice gates... he would create the most fertile floodplain in the region.
And the limestone? That meant cement. Roman concrete. The technology had been largely lost or ignored in this region, but the chemistry was simple.
"Give me the quill," Julian said.
Prince Louis snorted. "Going to sign your death warrant? Make sure you spell your name right, brother. We wouldn't want the inheritance to get tied up in court when the wolves eat you next winter."
Julian ignored him. He dipped the quill in the inkwell. But instead of signing the bottom of the deed immediately, he pulled a scrap piece of parchment the back of a dinner menu toward him.
"Cardinal, the tithe required by the Crown for this Barony... it is set at fifty gold florins annually?"
"A formality," Orsini waved his hand dismissively. "No one expects Grimwall to produce fifty florins. The arrears will simply accumulate until the land is repossessed."
"And if I pay double the tithe within two years?" Julian asked, sketching rapidly. "Would the Crown grant me autonomy over the forestry rights and mineral extraction for the next ten?"
Louis burst out laughing, spilling a drop of wine on his silk doublet. "Double? You won't be able to grow turnips, let alone mint gold! Orsini, humor him. Let him have his fantasy."
"If you can achieve such a miracle," Orsini said, his eyebrows raising as he watched Julian's hand move, "The Emperor would likely grant you anything you wished. But let us be realistic..."
The Cardinal stopped talking. He leaned in closer.
Julian was drawing. On the parchment, a complex yet elegant diagram was taking shape. Julian sketched the cross-section of the river valley. He drew a series of triangles and circles symbols representing vector forces and flow rates.
Bernoulli's principle, Julian thought. If I narrow the channel here, the velocity increases, flushing out the silt naturally.
He quickly sketched a waterwheel not the undershot wheels common in this era, but an overshot wheel with curved buckets, geared to a cam shaft. It was a design that wouldn't become common for another hundred years.
"What is this?" Orsini asked, his voice dropping to a whisper.
"A plan," Julian said absently. "Cardinal, you said the land is useless because of the water. But water is energy. If we channel the Serpentine here, we don't just drain the swamp. We power mills. Sawmills. Gristmills. Trip hammers for forging."
He looked up, his eyes locking with the Cardinal's. "It's an industrial engine waiting for a starter."
Louis walked over, squinting at the paper. He saw the geometry, the precise angles, the strange notations that looked like Greek but were actually calculus shorthand Julian had used out of habit.
"What gibberish is this?" Louis scoffed, though a flicker of unease passed through his eyes. "Since when do you know about... construction? You spent the last five years drunk in brothels."
Julian froze. Right. Cover story. He couldn't say, 'I learned this while studying for my PhD in Aerospace Engineering at MIT.'
"I... read," Julian lied smoothly. "In the Vatican library. While I was... repenting for my sins. Old Roman scrolls. Vitruvius. Archimedes."
Cardinal Orsini looked from the sketch to the Prince. The drawing was too confident, too precise. It spoke of a mind that saw the world not as it was, but as a series of problems to be solved.
"This mechanism..." Orsini pointed to the gear ratio Julian had scribbled. "It would tear a wooden axle apart."
"Not if we use iron-shod axles and lubricate with animal fat," Julian countered instantly. "And we don't build the gears out of oak; we use hornbeam or cast bronze if we can find the ore."
Orsini stared at him. The boy who was known for passing out in fountains was discussing metallurgy and mechanical engineering with the ease of a master craftsman.
"Your Highness," Orsini said slowly, "If this... thing actually works..."
"It will," Julian said. He grabbed the official deed to the Barony of Grimwall.
He thought of the oxygen warning. He thought of the cold. He thought of the helplessness of dying in a tin can a quarter-million miles from home.
The Middle Ages were dirty, brutal, and ignorant, but they were malleable. He had the sum of human knowledge from the next seven hundred years locked in his brain. He signed his name with a flourish: Baron Julian von Grimwall.
"I'll take the land," Julian said, standing up and handing the parchment to the stunned Cardinal. "And Louis?"
The arrogance on his brother's face had faltered, replaced by a confused frown. "What?"
"Keep the wine," Julian said, a small, dangerous smile playing on his lips. "You'll need it when you see what I export from my 'swamp' in six months. I suggest you invest in lumber futures now."
He turned on his heel and walked toward the heavy oak doors.
"Wait!" Orsini called out, clutching the sketch Julian had left behind. "This notation... the delta symbol... what does it signify?"
Julian paused at the door. He realized he'd written $\Delta P = \rho g \Delta h$ next to the dam sketch.
"It stands for 'Change'," Julian said, pushing the doors open. "And a lot of it is coming."
As the doors closed, leaving the Cardinal and the Prince in stunned silence, Julian let out a breath he felt he'd been holding since he died on the moon.
He grinned. It was good to be breathing oxygen again.