The third category in zither, chess, calligraphy, and painting was calligraphy.
They said that seeing one's writing was as good as seeing one in person. In the Nine Provinces, one would be mocked for not having good handwriting.
If a person wanted to become good at calligraphy, they'd require time and determination. However, it'd be too simple if it was purely a competition in calligraphy. After all, all of the princes and princesses were good at it.
To add points to 'good calligraphy' and allow it to be passed down through the times, one would naturally require to complement it with a good article.
Therefore, the Qi Emperor would come up with the topic for the Calligraphy Battle. The princes and princesses needed to write a good article based on this topic.
The one with the better article would naturally be the winner.