Emperor Gaozong of the Tang Dynasty, Li Zhi, was often too ill to attend court.
Another time, he suffered a severe bout of rubella, leaving him dizzy, weak, and unable to hold court. As days passed, memorials piled up like a mountain, and state affairs became a tangled mess.
Empress Wu Zetian, known for her sharp mind and decisive action, believed state affairs could not be left unattended, so she personally reviewed all memorials and made every decision, from the greatest to the smallest, herself.
During the Linde era of the Tang Dynasty, Shangguan Yi, a former imperial advisor in the Hongwen Academy and Vice Minister of the West Terrace, had long incurred the Empress Wu Zetian's displeasure. When he was accused of conspiring with the deposed Crown Prince Zhong, Wu Zetian saw her chance and ordered his execution.
When Empress Wu Zetian discovered the memorial accusing Shangguan Yi of treason, she showed no mercy, immediately issuing an edict to throw him into the imperial prison, confiscating his entire estate, and ultimately torturing him to death.
The death of Shangguan Yi cleared the final obstacle for Wu Zetian's regency. From then on, whenever Emperor Gaozong held court, Wu Zetian would sit behind a curtain suspended behind the imperial throne, handling all matters of state, large and small.
Both inside and outside the court, Wu Zetian and Emperor Gaozong of Tang were jointly called the "Two Saints." Later, the idiom "ruling from behind the curtain" came to refer to an empress or empress dowager managing state affairs from behind the throne.
Source: *Old Book of Tang*, Chapter "Annals of Gaozong II"
Meaning of the Idiom: Later, the Chinese idiom "垂帘听政" came to describe an empress or empress dowager managing state affairs from behind the throne.