‘And if we take stone for our own use we’ll lose that profit, you mean?’

‘Yes, in business that’s how one has to think.’

‘That’s true. But if we didn’t own these quarries, I would have paid for the stone in any case. Now we can save that expense. One also has to think like that in business.’

‘Then the question remains whether it’s wise to spend so much wealth building for war when there is peace,’ Eskil sighed, displeased that for once he was making no headway with his explanations of how everything in life could be calculated in silver.

‘In the first place, we’re not building for war but for peace. When there is war one has neither the time nor the money to build.’

‘But if war doesn’tcome,’ Eskil argued, ‘then haven’t all these efforts and expenses been to no avail?’

‘No,’ said Arn. ‘Because in the second place, no one can see into the future.’

‘Nor can you, no matter how wise you are in all matters concerning war.’

‘That’s quite true. And that’s why it’s the wisest course to build strong defences while we have time and peace prevails. If you want peace, prepare for war. Do you know what the greatest success of this construction would be? If a foreign army never pitches camp outside Arnäs. Then we will have built our defences as we should.’

Eskil was not entirely convinced, but a seed of doubt had been sown. If they could truly look into the future and see that the time of war was past, then strengthening their fortifications as Arn planned would not be worth all the effort and silver.

As things now stood in the kingdom, it looked as though the time of war was indeed past. Going back to the very beginning of the sagas there had never been a longer peace than under King Knut.

Eskil realized that he now wanted to exclude war as a means to be used in the struggle for power. He would rather see the sort of power that came from putting the right sons and daughters into the right bridal beds, and he would rather see the wealth created by trade with foreign lands as a protection against war. Who would want to demolish his own business? Silver was mightier than the sword, and men who had married into each other’s clans were loath to take up the sword against each other.

This was the wise manner in which they had sought to arrange things during King Knut’s reign. But no one could be completely secure, because no one could see into the future.

‘How strong can we make the castle at Arnäs?’ he asked, emerging from his long reverie.

‘Strong enough that no one can take it,’ replied Arn confidently, as though it were a given. ‘We can make Arnäs so strong that we could house a thousand Folkungs and servants within the walls for more than a year. Not even the most powerful army could endure such a long siege outside the walls without great suffering. Just think of the cold of winter, the rains of autumn, and the wet snow and mud of spring.’

‘But what would we eat and drink for so long a time?’ Eskil exclaimed with such a terrified expression that Arn had to give him a broad smile.

‘I’m afraid that the ale would be gone after a couple of months,’ said Arn. ‘And towards the end we might have to live on bread and water like penitents in the cloister. But we’d have a water supply within the walls if we dug a couple of new wells. And the advantage of grain and wheat, the same as dried fish and smoked meat, is that they can be stored for a long time in great quantities. But then we’d have to build new types of barns out of stone, which would keep all moisture out. Storing up such supplies is as important as building strong walls. If you then keep strict accounts of what you have, it’s possible that you might even be able to brew new ale.’

Eskil felt instant relief at these last words from Arn. His suspicion began to change into admiration, and with increased interest he asked how war was conducted in France and the Holy Land and Saxony, and in other countries that had bigger populations and greater riches than they did up here in the North. Arn’s replies took him into a new world, in which the armies consisted mostly of cavalry and in which mighty wooden catapults hurled blocks of stone against walls that were twice as high and twice as thick as the walls of Arnäs. Finally Eskil’s queries grew so importunate that they stopped to take a rest. Arn scraped away leaves and twigs from the ground next to a thick beech tree and smoothed out the area with his steel-clad foot. He bade Eskil sit down on one of the tree’s thick roots and called to the monk, who bowed and then took a seat next to Eskil.

‘My brother is a man of affairs who wants to create peace by using silver. Now we have to tell him how to do the same thing with steel and stone,’ Arn explained. He drew his dagger and began drawing a fortress in the brown dirt he had smoothed out.

The fortress he drew was called Beaufort and was located in Lebanon, in the northern reaches of the kingdom of Jerusalem. It had been besieged more than twenty times for varying periods, several times by the most feared Saracen commanders. But none had been able to take it, not even the great Nur al-Din, who once made the attempt with ten thousand warriors and kept at it for a year and a half. Both Arn and the monk had visited the fortress of Beaufort and remembered it well. They helped each other recall the tiniest details as Arn sketched in the dirt with his dagger.

They explained everything by turns, starting with the most important facts. The location was crucial, either up on a mountain like Beaufort or out in the water like Arnäs. But no matter how good the position for defensive war, they needed to have water inside the walls, not a spring outside that the enemy could find and cut off.

Equally important as access to water and a good position was the ability to store sufficiently large supplies of food, most importantly grain for bread and fodder for the horses. Only then could they begin to think about the construction of the walls and moats that would prevent the enemy from raising siege towers or bringing up trebuchets to fling stones and offal into the castle. And the next most important thing was the placement of the towers and firing positions so that they could cover all the angles along the walls with as few archers as possible.

Arn drew towers that protruded beyond the walls on every corner, explaining how from such towers they could shoot along the walls and not merely outward. In this way they could minimize the number of archers needed up on the ramparts, which would be a great advantage. Better shooting angles and fewer archers were essential.

Here Eskil interrupted, a bit reluctant to show his ignorance at not understanding the advantage of having fewer archers, which seemed to be a given for Arn and the monk. What did they gain by reducing their forces atop the walls?

Endurance, Arn explained. A siege was not like a three-day banquet. The point was to endure, not to let weariness reduce their vigilance. Those who laid siege to a castle wanted to take it by storm in the end, if not by negotiation. The besiegers could choose any time at all: after a day, a week, or a month; in the morning, at night, or in the broad daylight of the afternoon. Suddenly they would all appear at the walls with siege ladders, coming from every direction simultaneously, and if they had been diligent in hiding their intentions the defenders would be taken completely by surprise.

That was the decisive moment. Then it would be crucial that the defenders positioned up on the walls would have been on duty only a few hours. And that two-thirds of the defending force were rested or sleeping. When the alarm bell rang it should not take many seconds before all those who had rested were at their battle stations. If they practiced this several times, the defensive force of the castle would increase from one-third to full force in the same time it took the attackers to bring forward their siege ladders. So sleep was an important part of their defence. With this arrangement they also saved many sleeping berths, since a third of the defenders were always on the walls. And they also had a spot warmed up when they came down from duty.