This fifth installment of our What The Rivers Remember series follows On The Oise, Joan Of Arc, The River That Shaped Europe: Sailing Eleanor Of Aquitaine’s Bordeaux, The Seine: Richard, Monet and the Chalk Cliffs of Normandy and The Rhône and Saône: Caesar, Hannibal and the Roman Corridor, which left us among Roman ruins at Arles, the empire’s stonework still standing two thousand years on. This one moves north and forward six centuries, to a river an emperor made his own front yard — and to the treaty, drawn up by his grandsons, that turned it into a border instead.

Charlemagne did not build his capital on the Rhine. He built it a day’s ride west of it, at a cluster of Roman hot springs called Aachen, and then spent the next four decades using the river as the highway that let him govern, fight and hold together an empire bigger than anything Western Europe had seen since Rome itself. When he died, his empire held. When his grandsons divided the empire thirty years later, they placed the Rhine at the center of a contested middle kingdom—setting in motion the struggle over where France ended and Germany began that would continue for centuries.

A Capital at the Hot Springs

Charlemagne — Charles the Great, born around 747 by the most commonly cited estimate, king of the Franks from 768 — spent the first half of his reign on the move, the way Frankish kings always had, carrying the court from one royal estate to the next. By the late 790s he had stopped moving. He chose Aachen, a former Roman spa town prized since antiquity for its hot springs, and by 807 it functioned as the fixed capital of an empire that stretched from the Pyrenees to the Elbe. Contemporaries, not entirely joking, called it a second Rome.

He built to match the title. The Palatine Chapel, consecrated in 805, took its octagonal plan from the Basilica of San Vitale in Ravenna — Charlemagne had seen it, or heard enough about it, to want Aachen’s centerpiece to echo Byzantium’s most famous domed church, a deliberate claim to Rome’s inheritance in stone. The architect, Odo of Metz, built it to hold a throne of plain marble slabs in a gallery above the nave, reachable by six steps, positioned so the emperor could look down across the altar at Mass. That throne is still there. So, since 814, is Charlemagne himself, in a gold reliquary shrine added three centuries after his death, inside the chapel that is now the core of Aachen Cathedral — a UNESCO World Heritage Site and, for nearly six hundred years afterward, the coronation church of German kings. Thirty-one of them were crowned on that same hilltop between 936 and 1531, sitting, some of them, in Charlemagne’s own chair.

Aachen was more than a church and a throne. Charlemagne brought scholars to it — Alcuin of York chief among them — and used the palace school to drive what historians now call the Carolingian Renaissance: manuscripts copied and corrected, classical texts preserved that would otherwise have been lost, a clear, legible handwriting standardized across the empire that later gave Renaissance printers their model for the Roman typeface still in use today. He was, by Einhard’s account, an enthusiastic swimmer who used the hot springs daily and sometimes invited a crowd of a hundred courtiers into the water with him. It is a small, human detail to survive alongside the empire and the throne — a tall man for his century, just over six feet by the 1988 forensic study of his exhumed bones, doing laps with his own court in the water that gave the city its reason for existing in the first place.

The Frontier He Pushed to the Elbe

The empire Charlemagne ran from Aachen was not won by staying home. Starting in 772, he turned his army against the Saxons, a pagan confederation occupying the forests and plains east of the Rhine, in a war that would run, with truces and betrayals on both sides, for more than thirty years. It was, by his own biographer’s account, the longest and most brutal campaign of his reign. Frankish armies crossed the Rhine at Mainz repeatedly, marched into Saxon territory, burned the sacred pillar the Saxons called the Irminsul to prove their gods could not protect them, and returned home each time only to find the revolt they thought they’d ended waiting for them the following spring.

The war’s darkest single episode came in 782 at Verden, where Charlemagne is recorded — by the Royal Frankish Annals, a source not inclined to flatter his enemies — to have ordered the execution of 4,500 Saxon prisoners in a single day, in reprisal for an ambush that had killed a Frankish force days earlier. The number is disputed by modern historians, but the massacre itself is not; it stands as the ugliest entry in a war whose declared purpose was conversion. Charlemagne backed the sword with the font: subject Saxons faced death for refusing baptism, for cremating their dead in the old pagan rite, for eating meat during Lent. By 804, the fighting had ended and the frontier of Charlemagne’s empire had moved from the Rhine to the Elbe, absorbing the entire block of territory between the two rivers into Francia and, eventually, into Christian Europe. The river that had once marked the edge of the Roman world became, under Charlemagne, a road running through the middle of his.

A Palace on the River Itself

If Aachen was Charlemagne’s capital, Ingelheim was his address on the Rhine proper — a palace complex begun around 774 on a bluff above the river’s western bank, roughly nine miles from Mainz, with a view across the Rhine plain wide enough to double as a statement of power. Einhard ranked it, in his life of the emperor, alongside Aachen’s chapel and the palace at Nijmegen as one of Charlemagne’s three great building projects. Its Aula Regia, the great hall where the emperor received envoys and held court, was modeled directly on the fourth-century Roman basilica at Trier — another calculated echo of the empire Charlemagne wanted his own to be seen as continuing, not replacing.

Ingelheim outlived its builder as a working palace. Louis the Pious, Charlemagne’s son and heir, was born there in 778 and returned repeatedly to hold assemblies through his own reign. Little of the original complex still stands above ground — centuries of quarrying for building stone reduced most of it to foundations, rediscovered and excavated only in the 20th and 21st centuries — but the site, a short detour from the river towns cruise ships call at between Mainz and Bingen, marks the spot where Charlemagne’s government and the Rhine itself were, for once, in the same place at the same time.

The Border His Grandsons Drew

Charlemagne died at Aachen on January 28, 814, and was buried inside his own chapel. The empire he left behind lasted one generation intact under his son, Louis the Pious, and then came apart in the hands of Louis’s three sons, who spent the years after their father’s 840 death fighting a civil war over the inheritance. They ended it on August 10, 843, at Verdun, with a treaty that split the Carolingian empire into three kingdoms running north to south: West Francia for Charles the Bald, roughly the outline of modern France; East Francia for Louis the German, roughly the outline of modern Germany; and, wedged between them along the Rhine’s own length, Middle Francia for the eldest brother, Lothair — a long, awkwardly shaped strip running from the Low Countries down through Aachen, the Rhineland and Burgundy to Italy, built specifically so Lothair would keep both imperial capitals, Aachen and Rome, inside his own borders.

Middle Francia did not last. It fractured again within a generation, and the Rhineland corridor at its center — the region historians still call Lotharingia, a name that survives, worn down by a thousand years of pronunciation, in “Lorraine” — spent the next millennium as exactly what Verdun had made it: contested ground between the kingdoms on either side. Louis the German’s East Francia took the territory east of the Rhine outright and the dioceses of Speyer, Worms and Mainz on the river’s western bank besides, meaning the boundary between the two future nations never quite matched the river itself — a mismatch that helped fuel a rivalry over the Rhineland running from the medieval empire through Louis XIV’s wars, Napoleon’s annexations, and, finally, Alsace-Lorraine changing hands four times between France and Germany across 1871, 1918, 1940 and 1945. Charlemagne spent his reign making the Rhine a road through the center of one empire. His grandsons, splitting that empire three ways, are the reason it spent the next eleven centuries as a border instead — and why calling this stretch of water “the river that shaped Europe” is not really an exaggeration.

The Rhine Today: Where River Cruises Sail

The Rhine is the workhorse of European river cruising, and itineraries run its length from the Dutch delta to the Swiss border, most commonly Amsterdam to Basel or the reverse, seven or eight nights. AmaWaterways, Viking, Uniworld, Scenic, Avalon Waterways and CroisiEurope all sail it, usually threading Kinderdijk’s windmills, Cologne’s Gothic cathedral, Koblenz at the Moselle confluence, the castle-lined Rhine Gorge around the Loreley, Rüdesheim, Speyer and Strasbourg before turning up the river toward Basel.

Aachen sits far enough off the water — roughly 45 miles from Cologne — that it shows up on itineraries as an optional excursion rather than a port call, typically offered from Cologne or Düsseldorf for travelers willing to trade a few hours on board for a look at Charlemagne’s throne and the mosaic-covered dome above it. Mainz and the river towns near it put Ingelheim within easy reach for anyone who wants the palace instead of, or alongside, the chapel. Viking’s Rhine Getaway runs Amsterdam to Basel by way of Cologne, Koblenz, Speyer and Strasbourg; AmaWaterways pairs the Rhine with the Moselle on an 11-night itinerary out of Amsterdam with full days built in at Cologne. None of the standard itineraries call at Aachen or Ingelheim directly — this is a river whose Carolingian history takes a short detour to reach, unlike the Roman ruins standing right on the Rhône’s banks farther south — but for travelers willing to take the detour, the emperor who built Europe’s first great post-Roman capital, and the border his grandsons drew, are both within a short bus ride of the water.

What The River Remembers

Charlemagne spent his reign turning the Rhine into a road — a river he crossed to fight the Saxons, built beside at Ingelheim, and governed from a capital just off its banks, all in service of one empire he meant to last. Less than thirty years after his death, his grandsons began turning that same stretch of water into something closer to a wall, a border between kingdoms that, in one form or another, has outlived every empire built along it since, Charlemagne’s included.

That is the thread running under all five installments of this series so far. Rivers do not choose what they become. People do that, one generation deciding a river is a road and the next deciding it is a border — and the water just keeps running, carrying both decisions at once, indifferent to which one wins.

Next: the Danube, where the Habsburgs governed a continent that refused to speak one language.

About This Series

What The Rivers Remember is an ongoing series exploring the people and forces that shaped Europe’s great waterways — the queens, soldiers, emperors and explorers whose stories are written into the rivers that river cruisers sail today. Each installment follows one river, or a constellation of rivers, tracing European history from the water rather than the shore excursion. [Read the series introduction → What The Rivers Remember]

Articles in this series:
— The River Remembers: On The Oise, Joan Of Arc
— Bordeaux River Cruise: Eleanor Of Aquitaine’s Story
— The Seine: Richard, Monet and the Chalk Cliffs of Normandy
— The Rhône and Saône: Caesar, Hannibal and the Roman Corridor
— The Rhine: Charlemagne, the Border That Shaped Europe
— The Danube: The Habsburgs and the Connected Continent
— The Douro and Tagus: Henry the Navigator and the Edge of the Known World
— The Sources: Where Europe’s Rivers Begin — coming soon