Capitalized numbers are a unique way of writing numbers in China. Use Chinese characters with the same pronunciation as numbers instead of numbers to prevent them from being tampered with. According to textual research, capitalized numbers were first invented by Wu Zetian and later improved by Zhu Yuanzhang.
Extended data:
Whether Arabic numerals (1, 2, 3 ...) or Chinese lowercase numerals (1, 2, ...) are easy to be altered and tampered with because of their simple strokes. Therefore, the numbers on general documents and commercial financial bills should be capitalized in Chinese characters: one, two, three, four, five, six, seven, eight, nine, ten, one hundred, and one thousand (the strokes of "ten thousand, one hundred, and one trillion" are complicated, and there is little chance of using them, so there is no need to replace them with other words).
For example, "3,564 yuan" is written as "3,000 Wu Bai and 64 yuan". These Chinese characters have existed for a long time, and they are used as capital figures and belong to borrowing. The complicated writing of this number was fully used as early as the Tang Dynasty, and then it was gradually standardized as a set of "uppercase numbers".
References:
Baidu Encyclopedia-Capital Numbers