Size Matters: The Vikings, the Siege of Paris and the Bridge at Pontoise.

in 885, the Northman Sigfried and 40,000 Vikings ascended the Seine river in 700 boats and besieged the glimmering city of Paris for nearly a year, only deigning to depart after Charles the Fat paid them 700 lbs of silver.

Almost ever since, scholars have attempted to use these numbers to answer an important question; how large were the Viking invasions of the ninth century? Were they as one German scholar so eloquently penned, a

mighty eruption… a new German Völkerwanderung…which with iron force impacted the course of European history”?[1]

Or were they,

little more than groups of long-haired tourists who occasionally roughed up the natives?”[2]

In 1988, Carroll Gillmor applied sachkritik (a critical study of physical parameters) and Verbruggen’s theory of ‘operational space’ (the limitations of geography, topography and space on physical operations) to the question of Viking numbers at the Siege of Paris.

To sum up her thesis, she argued that if one applies these methods to Abbo’s figures, one must conclude, that more reasonable numbers for ships and men would be 300 vessels of various size, and a range of between 5000 and 8,000 men.

She further argued that if we examine the logistical requirements — food and water — for these new numbers and compare them with what we know, or can reconstruct of agricultural production in 9th century France, then these numbers should be reduced even further, to something in the hundreds “or even less”.[3]

The Mystery of the Bridge at Pontoise

After reading her article, something about the route to Paris caused me to ponder; for after sailing nearly all the way to Paris on the Seine, the Vikings turned up the Oise River to besiege a fortified bridge at Pontoise, which may have taken them a month or more to accomplish.

I asked myself;

Why did they do this?

And why did Charles the Bald fortify it, seemingly just before they got there?

It just makes no sense — if you’re a bunch of blood-thirsty Vikings, bent on plunder, and obviously heading for Paris — to take a detour, up a tributary to enact a siege on a small fortified bridge, that isn’t in your way!

There were other fortified bridges on the Seine River, that they surely must have dealt with, and for those, they had no choice. Either you destroy them, or park your boats and start walking. But the town of Pontoise is not on the way to Paris, if you’re sailing up the Seine, that is. So why bother assaulting this bridge?

The answer, as I discovered, has to do with the reason the bridge was there in the first place, and why it was fortified.

I looked at a map of the Seine, the one that Gilmor had provided, and I saw the little dot denoting Rouen’s position, and the dot representing Pontoise, and an idea came to me.

I wonder” I said to myself, “if there isn’t a road connecting those two points?

I knew that Pontoise, meant ‘bridge on the Oise,’ in Latin, so that suggested that the place and the bridge, or the bridge sight, at least, were ancient.

I knew that this area was once part of Roman Gaul, thanks to Julius Caesar’s murderous campaign through the same area before he was perforated by his fellow Romans on the Ides of March. The Romans loved to build roads and bridges, and they hated curved lines, because roads, you see, were built by and for Roman armies. They wanted the fastest route between two points.

If you study Roman roads, or just look at a map of them, all over the Empire, you will see hundreds of straight lines radiating out from the center: Rome. If there was a mountain in the way, go straight over it. If you can’t do that, dig THROUGH IT.

So I went to the library — that place where they have physical books — and found a copy of an atlas on Roman roads. And sure enough, there it was, straight as an arrow flies: a road, linking Rouen and Pontoise. As you can see on the map, the road from Rouen to Paris, runs directly over this bridge. But why would securing or taking this bridge matter to the Vikings sailing in ships to Paris? As I said, it was not in the path of their ships.

The Annals of St-Vaast held the secret: apparently, this particular Viking force had a land component, foot soldiers, probably attempting to use this road. This Viking land force was marching from Rouen where they had crossed the Seine by means of stolen boats. Why did they need stolen boats? Because they were on foot, and their ships had not yet arrived, as Vaast informs us:

because their ships (naves) had not arrived, they crossed over the river Seine in ships/boats (navibus) they discovered in the river.”[4]

Why had the ships not arrived? As professor Gillmor demonstrated in her article, the curvy nature of the Seine means that ships must travel longer distances than on the roads. The road from Rouen to Pontoise is a straight shot and you can bet your bottom dollar that the Vikings new it was there. Not only did they realize its strategic significance, so did Charles the Bald (who may have constructed this fortification), and his son, Charles the Fat, who was the king of the Western Franks in 885.

It also appears that while the Vikings were taking and pillaging Rouen, Charles the Fat may have been fortifying the bridges at Paris and at Pontoise:

“Again the Franks prepared to resist them, but not in combat,but they built fortifications, which blocked passage of those ships.They also erected a castrum (fortification) on the river Oise, in the place called Ad pontem Hiserae (Pontoise).”

But why at Pontoise, and why then? After hearing of the attack on Rouen, Charles would know for sure now that a land force was attempting to use the road from Rouen to reach Paris. Of course, we do not know for sure when he built the bridge at Pontoise, and work had probably begun much earlier, but they were apparently still working on at least one of the bridges at Paris, because it had not been completed when the Vikings arrived.

[the Norsemen] drew near the tower of Paris,immediately and powerfully assailing and storming it,and because it had not been completely fortified, they thought to seize it with no delay.”[5]

It is plausible, if not provable, that the fortified bridge at Pontoise was constructed or at least completed as a direct result of the Viking land force in 885. But why did the Vikings need a land force anyway? Why not just sail up the river?

I suggest that there are two sound reasons: security and logistics. Securing Rouen and the road to Paris, means the land force could protect the northern flank and shield the existence of the slower moving ship force. The Rouen road runs much closer to the river than the southern roads, making communication between the detachments quicker and easier.
The ships in turn could give the land force a possible escape route if overwhelmed by an enemy land force, and assist in taking fortified bridges, the best example of the latter being the siege at Pontoise. We know the ships were almost certainly there, because the Vikings were able to surround the fortified bridge.

In the month of November the Norsemen advanced up the Oise and encircled the aforementioned castrum by siege, and withheld water from those who were shut in the castrum, and prohibited them to draw out water from the river, since they did not have another source.”[6]

If it was a bridgehead fort, as Gillmor suggested was the case at Pont de l’Arche[7] (a bridge further down river), then the only way to surround it would have been to be on both sides of the Oise. A land force, would not be able to cross the river unless they managed to steal boats again, (and it is unlikely that the garrison manning a newly fortified bridge would leave boats lying around for enemies to pick up and use to surround them), so it is reasonable to assume that the Viking fleet sailed up the Oise, and landed on the other side, as St-Vaast suggested.

Logistically, ships can carry heavy equipment, siege engines, cookware and the beginning supply of food, especially if a smaller crew were used, or if they brought larger boats, like the Viking merchant vessel, the knarr. They probably brought women with them as well, maybe as cooks, or for other things that armies require. In turn, the land force could supply the ships with foraged grain and meat. A similar land/ship strategy was employed in 883 in an attack on Lavier:

the Norsemen came in the month of October, enclosing Latverum with horsemen (equitibus) and foot-soldiers (peditibus) and with the necessary equipment (suppellecti). Their ships also advanced up the river Somme”[8]

It’s also apparent from this passage that the Vikings employed horses, most likely beasts that they had ‘liberated’ from Frankish servitude. With horses, the speed of information increases, and they would not need many, which would reduce the logistical demands, something that professor Gillmor astutely pointed out was a downside to using horses for large raiding parties. Just a few could keep contact with ships, arrange supply connections, scout for enemy forces and assist in timing their attack on Pontoise.

So what does all this mean?

Important and crucial to any attempt to calculate the numbers of men in any campaign, is to understand all the constituent components employed in that campaign. In this case, it also included a land-based element. The fact that it was land-based, also makes it exceedingly difficult to calculate, as we lack the benefit of Abbo’s exaggerated estimates of men, and there is no ship data to employ.

What do I propose?

I suggest that there are at least 3 scenarios:

Scenario 1. There were 5000- 8000 men, and about 300 ships as Gillmor first proposed, but half of the men were detached at the mouth of the Seine to march inland. The fleet rowed/sailed all 300 ships upstream with either skeleton crews, or as the German scholar, Walther Vogel suggested, they had double crews to start with, which would either double the number of men or halve the ships.

This scenario is unlikely for two reasons:
1. It seems unlikely that a skeleton crew could row upstream the entire way, even with tidal surges and a breeze, at some point the benefit of the surge ends and winds don’t always blow the way you want them to. Rowing against wind and current is very hard work indeed, as I can attest to. Real-time tests, in replica ships would have to be conducted to determine how feasible this would have been.
2. Vogel is probably wrong, at least if we take the example of Skuldelev 2, a ship found in Roskilde Fjord in the 50s and 60s. Even though professor N. Roger argued that it could have carried at least 80 men, the test voyage of the replica, in 2007–8 only carried 63, and one thing they complained about was the cramped space, so it is highly unlikely that 80 or more fully armed Vikings could travel in such a boat for long periods without chopping each other into tiny pieces.[9] Yes, it is distinctly possible that our modern concepts of personal space are different than those of sweaty Vikings in the 9th Century, but probably not that much different.

Scenario 2. A force of several hundred men accomplished all that Abbo and the Annals of St-Vaast attributed to the campaign of 885–7. I believe this was professor Gillmor’s position, if I read her correctly. This conclusion was based mainly on the logistical problems. I propose these low numbers are incorrect, at least for the Paris campaign, though they are probably an accurate estimate for many Viking raids and campaigns, at least in the ninth century. It simply stains credibility to believe that a few hundred Vikings could besiege the great city of Paris for 11 months, assaulting it on many occasions, and fending off two relief forces. The Franks, however weak one wants to argue they were, were not THAT weak. It begins to sound like so much protesting to support a preconceived assumption that the population of early medieval Europe was dreadfully small. It simply bends the evidence beyond the point of breakage.

Scenario 3. What I propose, because quite frankly I can do no better at present, is to accept Gillmor’s middle estimate of somewhere between 5000–8000 men, in 300 vessels, but to hypothesize that half of these ships were left with a small guard force at the mouth of the Seine while the crews marched inland on foot. This would mean that only some 150 vessels made it to Paris. Some of the land forces commandeered horses. Of course, there might have been 10,000 to 16,000 men in 600 vessels, with half of the vessels continuing inland, (figures still lower than Dr. Gillmor’s largest calculations, and in line with the number of ships she proposed theoretically could have made it to Paris) but at present, I don’t think that’s a tree limb I wish to dance upon.

Why do I think the middle numbers are more plausible?

There are too many things we still do not know about food production in the 9th century. For the time being I will defer to Dr. Gillmor’s computations of the agricultural surplus in the region, but suggest that a force on the move, like the Vikings on their way to Paris, would not be concerned with taking only the surplus, they would take it all, and somehow, I don’t envision them remembering to say ‘please’ and ‘thank you,’ as my mother always instructed me to do. This might be a serious hardship for the local population for a few days or weeks, but they would probably survive and recover, or move on to safer pastures, if not hacked to death and left in the smoking ruins of their homes, during the initial raid, of course.

The problem of logistics is more important when the army becomes stationary at Paris for nearly a year. Armies quickly exhaust local supplies when they sit still, one of the main reasons Robert E. Lee decided to invade the lush green fields of Pennsylvania in the summer of 1863, for instance. Norther Virginia had been picked clean of produce for a couple of years, while the Yankees were living in abundance! The Vikings, after a few months or more, would be in a simmer situation at Paris, and they lacked the benefit of industrial age railroads to bring them food from afar. We know the Vikings were there for 11 months, so they must have eaten something, and if I propose to support the larger numbers, then I must at least attempt to address the problem. I must confess that I cannot prove that such a supply of food existed, but respectfully, neither can anyone prove at present that it did not. Luckily, our main source, Abbo, comes to my rescue; at some point during 886, he claims:

The Danes crossed over the Seine and headed out for the Loire;they scoured the land between the two rivers for great booty.”[10]

Nirmal Das, (the translator), suggested that this was the moment that the Vikings portaged their boats around Paris, as Dr. Gillmor had suggested they did at the end of the Siege, but this is clearly not the case, for the siege continued to the end of 886, and Abbo says they returned to Paris with great hoards of livestock, some of which they stored, much to his displeasure, in the monastery of St-Germain. Speaking in the personified voice of Neustria he lamented:

my fields, abundant in pasture, once echoed with the bleating of driven sheep; my vales rang with the groans of young bulls; my deep groves responded with the hoarse bark of deer; my many forests were filled with the hard grunts of boars, But those Grim Danes robbed me of all these…Since the Danes could not pen all the beasts in the fields and meadows, they turned the sacred hall of Saint Germain into a stable.[11]

Of course, Abbo claimed that all these animals were struck dead and rotted, infested with worms as a punishment from God, but it is surely more likely that they died via the swing of a Danish axe or broadsword, and were enjoyed by a lot of sweaty, hungry Scandinavians. But they were apparently good little Vikings, because they remembered to drink their milk, for Abbo asks rhetorically,

how many teats of cows did they squeeze as they roved…?”[12]

I must admit I find the image of heavily armed Vikings milking cows, amusing, even more so because it’s probably true.

There seems to me to be enough evidence in the history of early warfare, of large armies, without formal organizational structures, that managed to travel long distances, successfully execute sieges and extricate themselves more or less intact: the army of the first Crusade comes to mind.

Did the Crusaders suffer depredations? We know they most certainly did, and it is likely that the Vikings did as well, but unfortunately we lack their side of the story, as we have for the Crusaders.

I’m inclined to think that the Vikings in 885 might have actually been better prepared than the crusaders, at least from a logistical standpoint. It’s certain they had better intelligence of the region to which they were traveling than the Crusaders did: some of the Vikings may have in fact been on earlier raids in the Seine. They certainly seem to have acted as if they knew where they were going when they took Rouen and secured the road to Paris, and at some point they must have known or discovered the fortified bridge at Pontoise before the majority of their force arrived, as they seem to have coordinated their land and naval forces to take it.

The second reason I think the Viking army at Paris must have been large, is that contrary to what some scholars have suggested, it seems to defy logic to imagine that an army of a few hundred men, or even 1000 could maintain itself on enemy soil for well over a year, without being completely annihilated, regardless of the effectiveness or ineffectiveness of the enemy’s military.

It might be possible for a force of that size to do this, if they were constantly on the move, avoiding conflict, as many earlier Viking forces certainly did. But the force at Paris was more or less stationary for a year. Not only were they stationary, but far from avoiding battle, they attempted numerous times to storm the fortifications of Paris, engaged two enemy relief forces, successfully seized Rouen and the fortified bridge at Pontoise, and later besieged Sens and ravaged Burgundy.

While I agree that the figures of 18,000–21,000 men that professor Gillmor derived from Abbo’s 700 ships is probably too large, I must respectfully disagree that bringing such a number is strategically unnecessary, as she suggested.

If the Vikings knew that there were 5000 defenders in the Ile-de-le-Cité, as it has been suggested, then, it could be argued that they needed such a large number to take the city. As professor Bernard Bachrach (my graduate advisor) has argued, a ratio of 4:1 is usually needed to successfully storm a well-fortified site.

Of course, I would have to concede then, that since the Vikings were un-successful in breaching the city defenses, that they may not have held such an advantageous ratio, whatever the population of the city.

The question of course is, how many defenders were really in Paris in 885? I cannot argue with the estimate of 5000, as I have yet to scrutinize the data on the population of Paris, but it may be that 5000 is incorrect, just as it is probably true that we may never know for sure.

Where does this all leave us in terms of numbers of Vikings?

Unfortunately, we may be back to square one, or at least two or three, and if we are not that far back it is entirely due to the thorough work of professor Gillmor. But now that the Annals of St-Vaast have demonstrated that there was a land force, it will be very difficult, if not impossible to definitively determine the size of that force, and therefore the total number of bloodthirsty Vikings at the Siege of Paris in 885.

What this does seem to suggest though, is that the Vikings were anything but mindless barbarians, with a lack of organization. They are not the sweaty, grunting barbarians with credit cards that we’re used to seeing on television. They knew where they were going and the best way to get there, and through sound strategic planning, they not only reached their goal, but also managed to feed their army, whatever the size, for over a year while maintaining a siege of a major Frankish city and then extricated themselves with pockets full of Carolingian silver: no mean feat for any army, large or small.

Enjoy this article?

Then you’re gonna love my next book! (June 11, 2017)!

Vikings, War and the Fall of the Carolingians!

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Love Vikings? Check out these articles:

[1] Vogel, 11.
[2] J. M. Wallace-Hadrill, 5.
[3] Gillmor, “War on the Rivers” 109.
[4] AV 885, Simson 57.
[5] AV 885, simson 58.
[6] AV 885, simson 58.
[7] Gillmor, Carroll, “The Logistics of Fortified Bridege Building on the Siene uner Charles the Bald” Anglo-Norman Studies XI Proceedings of the Battle Conference 1988, Ed. R. allen Brown, (Woodbridge, 1989).
[8] AV 883. Simson, 54.
[9] Andrew Curry, “Raiders or Traders?” Smithsonian, V. 39, n. 4, (July 2008): 24–30. You can also read the ships logs, of not only the captains, but the cook, nurse and some of the crew members online at:, accessed 5/1/09.
[10] Abbo, p 61.
[11] Abbo, p. 61, 63.
[12] Abbo, p 61.



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Steve Bivans

Steve Bivans

Mantra: Shireness to the World. Author of Be a Hobbit, Save the Earth, & The End of Fear Itself.