Article: Despite the continuing prominence of Nanjing (then known as Jiankang), the settlement of Qiantang, the former name of Hangzhou, remained one of the three major metropolitan centers in the south to provide major tax revenue to the imperial centers in the north China. The other two centers in the south were Jiankang and Chengdu. In 589, Qiangtang was raised in status and renamed Hangzhou.

Question: How many major metropolitan centers were there in the south at the time?
three