depicting Basil II and Constantine VIII, holding a cross.
Theodora was the third and youngest daughter of the Byzantine Emperor Constantine VIII and Helena, daughter of Alypius.:503 She was Porphyrogenita,:259 "born into the purple"; this was the appellation for a child born in the capital to a reigning emperor. Her father became co-emperor in 962 and sole emperor in 1025. His reign as sole emperor lasted less than three years, from 15 December 1025 to 15 November 1028.:503
As an eligible imperial princess, she was considered as a possible bride for the Holy Roman Emperor in the west, Otto III in 996.:253 However, Theodora was overlooked in favour of her sister Zoë. Otto III died before any marriage could occur.:259 Theodora's uncle Basil II prevented his nieces from marrying any of the Byzantine nobility, calculating that such a marriage would have given their husbands a claim on the imperial throne. As women, Theodora and Zoë were unable to exercise any state authority, their only say in this was in choosing, or more likely accepting or not, a husband who would acquire their authority upon marriage. Consequently, Theodora lived a life of virtual obscurity in the imperial gynaeceum (women's quarters).:269
Basil II died childless in 1025 and Constantine VIII became sole emperor at the age of 65. As he had no sons, Theodora and Zoë were catapulted into the centre of imperial politics.Romanos Argyros, stating that Romanos was already married – his wife having become a nun to allow Romanos to marry into the imperial family.:465 Theodora further claimed that since Romanos and she were third cousins, it was too close a blood relationship for marriage to occur.:270 Consequently, Constantine VIII chose Theodora's sister. Zoë married Romanos three days before her father died.
Intelligent and possessing a strong and austere character, Theodora defied her father by refusing to marry the man her father had chosen to succeed him,
Empress Zoë tonsures
her sister Theodora
With the accession of Romanos, Theodora prudently retreated back into the gynaeceum, with its daily religious routines,:276 but this did not save her from her sister's envy. Never forgiving Theodora for being their father's first choice, Zoë persuaded her husband to appoint one of his own men as the chief of Theodora's household, with orders to spy on her.:469 Shortly afterwards, Theodora was accused of plotting to marry Presian of Bulgaria and usurp the throne with him. Presian was blinded and sent to a monastery; Theodora was not punished. In 1031 she was implicated in a similar conspiracy, this time with Constantine Diogenes, the Archon of Sirmium.:627 Theodora was forcibly confined in the monastery of Petrion. During a visit, Zoë compelled her sister to take Holy Orders.:471 Theodora remained there for the next eleven years, as Zoë managed the empire with her husbands, Romanos III and, after his death, Michael IV.