In addition, in those days people had not called them 'Nanto Rokushu,' it was later used for distinguishing from 'Heian Nishu' (the Tendai sect and the Shingon sect) which flourished mainly in Heian-kyo (the capital of Japan in the Heian period) after the Heian period.
なお、当時からこう呼ばれていたわけではなく、平安時代以降平安京を中心に栄えた「平安二宗」（天台宗・真言宗）に対する呼び名である。