Small seal script
Small seal script, or xiaozhuang characters, was the first set of Chinese characters that were made the standard all across China. While they were not the first set of Chinese characters, they were the first set that were used universally all across Imperial China. It was made standard during the Qin dynasty (221 BC to 206 BC) because Emperor Qin Shi Huang wanted people all across China to be able to communicate with each other without confusion. Before the Qin dynasty united China, each of the Warring States had their own set of Chinese characters, which could not be understood by people from other states unless they had already learned them.
Since the strokes used to write small seal script characters were very long, curvy, and difficult to write quickly, officials of the Han dynasty replaced small seal script with traditional characters, which are still used today in China. However, since small seal characters look very artistic, they can still be seen in Chinese seals and calligraphy today.