Chapter Seventy-Seven: Stationed at the City Walls

In the blink of an eye, three months had passed. The development of Youzhou City gradually returned to normal, and everything was once more on track. The common people, eager for a bountiful harvest and a prosperous year ahead, worked diligently in the fields. Once desolate wheat fields were now covered with young shoots, as everyone strove to accumulate grain as soon as possible. With Guo Jia and Xu Maogong handling administrative affairs together, and Dian Wei and Ding Feng jointly commanding the army, order prevailed. Each morning, the rousing voice of the army’s song could be heard at dawn—a tradition Zifan had instituted to foster camaraderie among the soldiers.

Youzhou City had taken on a new appearance; everything was well-managed and orderly, and the streets regained their former bustle, displaying a scene of flourishing vitality.

Thus, during this period, Zifan, as the governor, lived in great comfort. At times, he would visit small taverns under the pretext of inspecting the people's livelihood, or wander through the pleasure quarters to feast his eyes, or spar with soldiers in the barracks. Now Zifan finally understood how the ancients managed to while away their days so easily—everywhere was awash in the light of spring.

A few days later, Guo Jia delivered the neatly organized reports to Zifan, but his face was hesitant, shadowed with heavy thoughts.

“What is it? Is there some difficulty?” Zifan looked up at Guo Jia. “There’s no need for you and me to be so circumspect.”

“My lord, two years ago, Youzhou’s borders suffered repeated invasions by the Yellow Turban Army, and the city walls have long since fallen into disrepair, no longer able to withstand foreign threats. Recently, many citizens have also reported frequent harassment from mountain bandits. Therefore, I propose building a new wall at the border to defend against the bandits and ensure the people’s safety. But I fear we cannot finish such a project in so short a time.” Guo Jia shook his head, sighing deeply.

“Oh? And how do you usually build city walls?” Zifan inquired.

“We construct them of rammed earth,” Guo Jia explained. “We use local yellow or black soil, compacting it layer by layer until each is about fifteen centimeters thick. To make the walls sturdy and durable, the outer face is not built straight up, but instead slopes inward at the top, forming what we call a ‘battered wall.’ The base is about four meters thick, narrowing to three and a half meters at the top, and the height varies between seven and ten meters. Such earthen walls are solid and highly defensible.

“At the city gates and corner towers, the walls are made even thicker. We build an arched tunnel at the base, then continue ramming earth above it. The top is paved with bricks, and pillars are erected to support a structure—a tower, which serves as both a marker visible from afar and a defensive fortification. From there, one can observe the enemy and shoot arrows. But constructing these walls requires an enormous amount of earth.

“And that’s just for the simplest walls. Brick or stone walls take even longer. For brick walls, we wrap the rammed earth core with layers of large bricks, which requires hundreds of masons to first chisel the stones into rectangles and then lay them piece by piece.” Guo Jia quickly added.

“So this is how you’ve always built city walls?” Zifan murmured, shaking his head. “It’s a complex project that demands a great increase in both manpower and resources.”

“Yes,” Guo Jia replied. “Every city wall has been built this way, never otherwise. The problem is that it takes at least two years and a huge number of craftsmen. Time is short and the city has only just begun to recover from devastation. To mobilize so many people now would be unwise.” Guo Jia sighed again.

Zifan stroked the stubble on his chin, nodding thoughtfully. “I see. If we want to build a wall quickly, we must use a more efficient method—perhaps even technology unknown to this era.

“Here’s what we’ll do: have the craftsmen set up a small processing plant next to the government office, then recruit a large workforce. Pay them daily wages, provide food and lodging, and send them to the southern mines to excavate according to the locations on this list. Pile the excavated earth to one side, then transport it to the processing plant for wall construction.” With the help of the system map, Zifan had even pinpointed nearby mineral deposits. Although high technology was not yet available, they could still assign laborers to work tirelessly, day and night.

Guo Jia looked down at the list, puzzled. “What will these minerals be used for?”

“They’re for making cement.”

“Cement? What is that?”

Zifan smiled. “It will speed up wall construction and bind stones together. I’ll write out detailed instructions for you on how to use it. You'll understand then.” Though Zifan spoke with confidence, Guo Jia remained skeptical, his face full of disbelief.

Cement, in fact, is simple to make. Limestone, clay, and iron ore powder are finely ground and mixed in certain proportions—this mixture is called raw meal.

Then, it is calcined at a temperature of about 1,450 degrees Celsius, producing what is known as clinker. The clinker is then ground together with gypsum in precise proportions, yielding cement. When mixed with water, cement forms a paste that hardens in air or underwater, binding sand, stone, and other materials into a solid mass.

This happens because the substances in the cement react with water, forming tiny crystals on the surface of the cement particles. These delicate crystals stick together through minute attractive forces, creating a network structure known as a “set structure.” Since these bonds are formed by weak, disordered forces, the initial strength is low and quite plastic.

When Guo Jia witnessed this so-called “cement” transform from liquid to solid overnight, producing extraordinary adhesion, his face showed utter disbelief and amazement.

For the people of this era, cement was already a marvel of advanced technology. Even more remarkable was its ability to take on any shape—no longer would craftsmen need to cut and polish stone. They could simply pour cement into a mold, let it set, and use the resulting blocks as bricks. This would eliminate time-consuming and laborious processing, greatly accelerating the construction of the city walls and speeding up the entire project.

“With enough workers, the wall could be finished in just half a year!” Guo Jia’s voice trembled. He hadn’t imagined such a wondrous material existed in the world, far surpassing his expectations.

From now on, the pace of all construction would increase dramatically. The process for making cement was extremely simple. “The great task of building the Great Wall will be entrusted to you in the future,” Zifan said, patting Guo Jia on the shoulder with a smile. “I trust you won’t let me down.”

“My lord, rest assured. I will accomplish this task,” Guo Jia replied, bowing deeply. Holding the cement instructions in his hands, he was utterly absorbed, studying them again and again.