When was the Xingtan built?

Song Zhenzong's "Confucius Temple Shoukong Minor" built an apricot altar to commemorate Confucius' lecture. The record of Yunzao can be found in Zhuangzi Ke Fisherman's Chapter:

Confucius swam in the shade forest and sat in the apricot altar. His disciples studied books, and Confucius played string songs and drums.

As for the position of the apricot altar before, it has been impossible to verify. Later, Daofu Kong, the 45th grandson of Confucius, supervised the restoration of the Confucius Temple. He expanded the hall and moved it back. On the basis of the old site, he "moved the land to an altar and planted apricots around it", that is, he built a earthen platform and planted apricot trees around it, named the apricot altar.