천자문
During Taejong's rule, improvements were made. Among the people responsible for the developments was Choe Hae-san, the son of the aforementioned Choe Mu-seon. The "cheon" "heaven" or "sky", "ji" "earth", "hyeon" "black", and "hwang" "yellow" or "gold" names are not significant, being the first four characters of the Thousand Character Classic, thus making them equivalent to Cannons A, B, C, and D. The following is a list some of the main cannons (called "hwapo" "fire gourd") of this time period: