Still he did not know what to do about Caris, and he fell asleep worrying.

Edmund woke him at first light. By then almost every cart in Kingsbridge was on the far side of the river, in a straggly line that led through the suburb of Newtown and half a mile into the forest. It took a couple more hours to ferry the people over. The excitement of organizing what was effectively a pilgrimage diverted Merthin’s mind from the problem of Caris and her pregnancy. Soon the pasture on the far side was a scene of good-natured chaos, as dozens of people caught their horses and oxen, led them to their carts and backed them into the traces. Dick Brewer brought over a huge barrel of ale and gave it away – “To encourage the expedition,” he said – with mixed results: some people were so encouraged they had to lie down.

A crowd of spectators gathered on the city side of the river, watching. As the line of carts at last began to move off, a great cheer went up.

But stones were only half the problem.

Merthin turned his attention to the next challenge. If he was to begin laying stones as soon as they arrived from the quarry, he had to empty the coffer dams in two days instead of two weeks. As the cheering died down, he raised his voice and addressed the crowd. This was the moment to catch their interest, when the excitement was fading and they were beginning to wonder what to do next.

“I need the strongest men left in town!” he shouted. They went quiet, intrigued. “Are there any strong men in Kingsbridge?” This was partly a come-on: the work would be heavy, but asking only for strong people also threw down a challenge that the young men would find hard to resist. “Before the carts get back from the quarry tomorrow night, we have to empty the water out of the coffer dams. It will be the hardest work you’ve ever done – so no weaklings, please.” As he said this, he looked at Caris in the crowd and caught her eye, and he saw her flinch: she remembered using that word, and she knew she had insulted him. “Any woman who thinks she is the equal of the men can join in,” he went on. “I need you to find a bucket and meet me on the shore opposite Leper Island as soon as possible. Remember – only the strongest!”

He was not sure whether he had won them over. As he finished, he spotted the tall figure of Mark Webber, and pushed through the throng to him. “Mark, will you encourage them?” he said anxiously.

Mark was a gentle giant, much liked in the town. Even though he was poor he had influence, especially among adolescents. “I’ll make sure the lads join in,” he said.

“Thank you.”

Next, Merthin found Ian Boatman. “I’m going to need you all day, I hope,” he said. “Ferrying people out to the coffer dams and back. You can work for pay or an indulgence – your choice.” Ian was excessively fond of his wife’s younger sister, and would probably prefer the indulgence, either for a past sin or for one he was hoping to commit soon.

Merthin made his way through the streets to the shore where he was preparing to build the bridge. Could the coffer dams be emptied in two days? He really had no idea. He wondered how many gallons of water were in each. Thousands? Hundreds of thousands? There must be a way of calculating. The Greek philosophers had probably worked out a method but, if they had, it had not been taught at the priory school. To find out, he would probably have to go to Oxford, where there were mathematicians famous all over the world, according to Godwyn.

He waited at the river’s edge, wondering if anyone would come.

The first to arrive was Megg Robbins, the strapping daughter of a corn dealer, with muscles enlarged by years of lifting sacks of grain. “I can outdo most of the men in this town,” she said, and Merthin did not doubt it.

A group of young men came next, then three novice monks.

As soon as Merthin had ten people with buckets, he got Ian to row them and him to the nearer of the two dams.

Inside the rim of the dam he had built a ledge just above water level, strong enough for men to stand on. From the ledge four ladders reached all the way down to the river bed. In the centre of the dam, floating on the surface, was a large raft. Between the raft and the ledge there was a gap of about two feet, and the raft was held in a central position by protruding wooden spokes that reached almost to the wall and prevented movement of more than a few inches in any direction.

“You work in pairs,” he told them. “One on the raft, one on the ledge. The one on the raft fills his bucket and passes it to the one on the ledge, who tosses the water over the edge into the river. As the empty bucket is passed back, another full one is passed forward.”

Megg Robbins said: “What happens when the water level inside falls, and we can’t reach one another?”

“Good thinking, Megg, you’d better be my forewoman in charge here. When you can no longer reach, you work in threes, with one on a ladder.”

She caught on fast. “And then fours, with two on a ladder…”

“Yes. Though by then we’ll need to rest the men and bring in fresh ones.”

“Right.”

“Get started. I’ll bring over another ten – you’ve got plenty of room still.”

Megg turned away. “Pick your partners, everyone!” she called.

The volunteers started to dip their buckets. He heard Megg say: “Let’s keep a rhythm going. Dip, lift, pass, chuck! One, two, three, four. How about a song to give us the swing of it?” She raised her voice in a lusty contralto. “Oh, there was once a comely knight…”

They knew the song, and all joined in the next line: “His blade was straight and true, oh!”

Merthin watched. Everyone was soaking wet in a few minutes. He could see no apparent fall in the level of the water. It was going to be a long job.

He climbed over the side and into Ian’s boat.

By the time he reached the bank there were thirty more volunteers with buckets.

He got the second coffer dam started, with Mark Webber as foreman, then doubled the numbers in both locations, then started replacing tired workers with fresh ones. Ian Boatman became exhausted and handed the oars over to his son. The water inside the dams fell inch by wearisome inch. As the level fell, the work went ever more slowly, for the buckets had to be lifted greater and greater distances to the rim.

Megg was the first to discover that a person cannot hold a full bucket in one hand and an empty one in the other and still keep balance on a ladder. She devised a one-way bucket chain, with full buckets going up one ladder and empty ones down another. Mark instituted the same system in his dam.

The volunteers worked an hour and rested an hour, but Merthin did not stop. He was organizing the teams, supervising the transport of volunteers to and from the dams, replacing buckets that broke. Most of the men drank ale during their rest periods, and in consequence there were several accidents during the afternoon, with people dropping buckets and falling off ladders. Mother Cecilia came to take care of the injured, with the help of Mattie Wise and Caris.

Too soon, the light began to fail, and they had to stop. But both coffers were more than half empty. Merthin asked everyone to come back in the morning, then went home. After a few spoonfuls of his mother’s soup he fell asleep at the table, waking only long enough to wrap a blanket around himself and lie down in the straw. When he woke the next morning, his first thought was to wonder whether any of the volunteers would show up for the second day.

He hurried down to the river at first light with an anxious heart. Both Mark Webber and Megg Robbins were there already, Mark eating his way through a doorstep of bread and Megg lacing a pair of high boots in the hope of keeping her feet dry. No one else showed up for the next half hour, and Merthin began to wonder what he would do with no volunteers. Then some of the young men arrived, carrying their breakfast with them, followed by the novice monks, then a whole crowd.