We will now talk about the structures of Cheomseongdae. Its height is 30.4 in dangchuk (old Chinese measurement scale), or 9.09 meters in today's measurements. The diameter of layer 1 is 4.93 meters, and the diameter of layer 27 is 2.85 meters. The area of the upper base layer is 5.18 square meters, and the height is 39.5 centimeters. The area of the lower base layer is 5.36 square meters, and the height is 39.5 centimeters. There are many arguments on the total number of stones in Cheomseongdae. Some say 365 and so on. Based on my observation, there are 404 granite stones as shown in the report by National Research Institute of Cultural Heritage. There are 20 stones at the base, 367 stones visible from outside in the body including 3 insert stones and 17 stones in #-shaped layouts at the top and inside including one flat stone. Often the insert stones are overlooked in counting. As you can see, these small insert stones, there are three of them. In total, 404 stones were used to build Cheomseongdae. Concerning the weight, the heaviest stone is 869 kilograms. Pretty heavy, right? And there are ones as light as 54 kilograms. On average, a stone block weighs 357 kilograms. The total weight is 264.5 tons. It's a structure of a significant weight. So, the pressure forced on the base is 9200 kilogram per square meter. When we look at the stones in the body, they are fan-shaped. In other words, the outside surface is neatly trimmed and polished. But the inside is, as you can see here on the right side, they are not trimmed but left in their original shape. However, this has an advantage. Friction between rough stones contributes to the stability of the structure. And at the very top, you can clearly see here fan-shaped stones. So the fan-shaped stones are arranged in this way. Next, let's look at each layer. This is the shape of the 5.3 square meter base layer. Then, the first layer with the diameter of 5.18 meters has stones arranged like shown in this slide. And likewise the 12th layer, the 14th layer, and then the 27th layer. The 27th layer has the diameter of 3.1 meters. However, it's not a perfect circle. And on the 29th layer, we can see the #-shaped arrangement. And, there is an important feature. One interesting thing about Cheomseongdae is that stones were built up to form a curve by using "Toemullim," one of the construction methods of corbelling. Hence, from the 1st layer to the 17th layer, we can see that this method of Toemullim was applied. Like shown here. And then, from the 18th layer to the 27th layer, they went up straight. The actual appearance is shown in this picture. This is the Toemullim section. And then the straight section is also shown. And when viewed from above, this is how Toemullim layers appear. And there is another important feature in Cheomseongdae. As mentioned on this slide, it's called "Bangteulsimsuk" (#-shaped stones), also known as "Binyeosuk" (hairpin stones). These stones are placed in the 25th and 26th layers in the shape of "#", similar to the top layers. Also, a Bangteulsimsuk is in the 9th layer as well. This arrangement is shown in this diagram. We can see that the stone is inserted inside Cheomseongdae in this way. So the pictures on the right side show how Bangteulsimsuks are placed inside. Here like this, in the shape of #. But they are one layer apart. Here as well. Arranged to form a # shape over different layers. So, if we show these in a diagram, this is how they are placed in the 25th layer, and like this in the 26th layer. When we look them together, they form one #-shaped structure. This greatly contributes in keeping Cheomseongdae stable. And interestingly, there is a window that opens to the southeast. This window has two stone posts keeping the opening that's 0.91 meters high. And the inside is filled with soil and pebbles up to the 12th layer. By the way, one very interesting structural characteristic is that instead of using mortar or those sorts, they used the dry construction method. And stones are supporting each other only by gravity and friction. Then, Toemullim. The aforementioned Toemullim method was applied. And, the #-shaped arrangement such as Bangteulsimsuk is also used. And, the compact filling of pebbles and soil up to the 12th layer has the function of lowering the center of the gravity of the structure. And then, as we saw, the window has two stone posts in the shape called lintel & posts. So the window of Cheomseongdae also plays a significant role in the structural stability. And originally, in the #-shaped arrangement at the top, there was iron devices called clamps that held the stones together. But now only one of them remains. And also, to form the # shape, they trimmed the stones to make cross lap joints. And the platform at the base supports the structure for stability. Therefore, the structural characteristics of Cheomseongdae altogether resulted in the most optimal design that's stable as well as beautiful. We can call it a masterpiece in construction. These contents are from the research of a Korean-American scientist. As you can see here, it comes down straight from the top. Then, there's a slight curve. From there, in a straight line again. And then, a curve. This curve is very mathematical. So the author of the article particularly calls this curve as the Silla curve in the paper. Look at the picture on the right. When they were building Cheomseongdae, they filled the inside with pebbles and soil. And then, as they built it up, they added on #-shaped arrangements, Bangteulsimsuk, to complete Cheomseongdae. This is what they say. And before they started building up Cheomseongdae, they made preparations below the base layers. They dug into the ground about 1.5 meters deep and filled it with pebbles, sand, and soil. On top of that, they laid the base layer and then Cheomseongdae. And they laid the #-shaped arrangement at the very top. All of these were done carefully and orderly. About this, then how did they actually built up Cheomseongdae? There's no theory or historical record. Many architectural engineers are looking into this. I'll talk about one of the modern research. As I have mentioned before, the stones are very heavy. So they got an idea from huge tombs around the Cheomseongdae site. To build a tomb, you have to pile up soil. Probably they used a similar method for Cheomseongdae. This is called the Soil Scaffolding Method. They began with putting down a base layer. And as they built on, they piled up soil around the structure. When it was the highest, the scaffolding probably resembled nearby royal tombs. So eventually, the scaffolding went up to the top. And afterwards, they dug out the soil, but left the soil in lower half. This is the Soil Scaffolding Method that some scholars claim that Silla people used.
