Heshun Building is completely built according to the "Bagua Diagram" layout of the Book of Changes. First of all, the circle can better reflect the concept of harmony and unity of heaven, earth and man. The Book of Changes emphasizes that "the sky is round and the place is round", "the circle is the sky and the appearance of the universe", and "heaven, earth and man are one".

The round tower has a prominent centripetal force and unity. The main building is divided into eight trigrams and eight major parts, which means Qian, Kun, Kan, Li, Zhen, Gen, Xun, and Dou Bagua. Between the hexagram and the hexagram build a blue brick fireproof partition wall, open an arch in the partition wall, close the door into a courtyard, do not interfere with each other, open the door is the whole building through, connected into a whole. The front door is "Xun hexagram", while the back door is "Qiangua".

There is a hall, two wells, three doors in the building, the two wells are secretly combined with the yin and yang poles in the "Bagua", the three doors are the main gate and the side door at both ends, which means that the heaven, earth and people in the gossip are three talents. The door of the building is exquisite, and the door of each house has a lintel and hall number. The door frame is hung with all kinds of gossip peace charms, upstairs and downstairs in addition to the exquisite carved windows, there are special gossip security guards tired of the meaning of the auspicious charm of the door and window paintings.

Shi Kang was surprised to measure the wall of the tulou with his palm, but he didn't expect the thickness to reach one meter, Dan Yan deliberately wanted to test him, "Do you know what material the wall of the tulou is made of?" ”

Shi Kang carefully distinguished, and replied confidently, "I guess it is a civil engineering structure building built with rammed walls of mud and sand ash, and the building materials are nothing more than some local stones, loess, fir wood, pebbles, ash, sand, green tiles, etc. ”

Dan Yan smiled proudly, "Your answer can only be half right, and you must not guess the key materials." ”

Shi Kang was puzzled, "What else could it be?" Is it difficult to use reinforced concrete? ”

Dan Yan raised his head and announced the answer, "The building materials of Tulou are very peculiar, mainly based on local clayey laterite, mixed with an appropriate amount of small stones and lime, repeatedly mashed, mixed well, and some key parts are also mixed with an appropriate amount of glutinous rice, brown sugar or egg whites to increase its viscosity." When ramming an earth wall, add some wood, bamboo or large rocks to the mud to strengthen the wall and increase its tensile force. After repeated ramming, an earthen wall like reinforced concrete was built, and the outside was smeared with a layer of weatherproof lime, and the roof was covered with fire-fired tiles, so that it was as solid as a rock, which could resist the attacks of wild beasts or thieves, and also had the functions of fire and earthquake resistance, as well as warm in winter and cool in summer. In the era when there was no reinforced concrete, the intelligent Hakka people used this seemingly almost primitive construction method to build a mysterious and huge tulou, which achieved a miracle in the history of architecture. ”

Shi Kang's jaw almost dropped in shock, "Are you sure this isn't a dark cuisine?" How can you build a house with brown sugar, glutinous rice, and egg whites? Aren't you afraid that the insects will gnaw away the wall? ”

Dan Yan laughed, "No, our tulou is solid." There is a Hakka proverb called 'a bowl of pork for a bowl of Sanhe soil'. It shows that the formula of soil used for the exterior wall of the tulou is really complex and elegant. First of all, its main building material must be fine red clay without impurities, and then mixed with fine river sand, silt from the bottom of paddy fields and old wall mud in a certain proportion. After stirring well, add water and use a hoe to turn and ferment repeatedly. This process is crucial to the construction of the tulou, and the full fermentation of the mixed mud will directly affect the service life of the tulou after completion. If the mud on the exterior wall of the tulou is not fermented properly, the wall will crack when the temperature and humidity change, threatening the safety of the residents in the tulou. At this time, the good red pond, the blistered egg white and the glutinous rice soup with no rice grains are added to the Sanhe soil, because there is a special proportion, so it is difficult to nail into it, not to mention insects. ”

Shi Kang rubbed the living fossils of this ancient earthen building with admiration, and found that the gate was nailed with steel plates, the top of the door was equipped with a water and sand leakage device to prevent fire, and there was a lookout at the top of the door to understand the enemy's situation. Dan Yan told Shi Kang that there are also underground tunnels hidden in the building, if you need to defend against the enemy, you only need to close the gate, a few young adults guard the gate, and the tulou is like a strong fortress, women and children can sit back and relax. Nowadays, Tulou is no longer a fortress, but those complete and exquisite defense facilities still surprise people.