起信論疏筆削記 4.6

4.6

大周者，以則天初載二年九月九日，改國號為大周，改元為天授元年，故曰大周則天也。

"Great Zhou": because on the ninth day of the ninth month in the second year of the Chuzao reign era, Zetian changed the dynastic name to the Great Zhou and altered the reign era to the first year of Tianhou, she was therefore called "Zetian of the Great Zhou."