In the 940s or 950s, probably around 954 or 955, after the Rus'–Byzantine War of 941 and the death of the Grand Prince of Kiev, Igor I (), his widow Olga of Kiev – regent for her infant son Sviatoslav I () – visited the emperor Constantine VII and was received as queen of the Rus' in Constantinople. She was probably baptized in Hagia Sophia's baptistery, taking the name of the reigning "augusta", Helena Lecapena, and receiving the titles "zōstē patrikía" and the styles of "archontissa" and hegemon of the Rus'. Her baptism was an important step towards the Christianization of the Kievan Rus', though the emperor's treatment of her visit in "De caerimoniis" does not mention baptism. Olga is deemed a saint and equal-to-the-apostles () in the Eastern Orthodox Church. According to an early 14th-century source, the second church in Kiev, Saint Sophia's, was founded in "anno mundi" 6,460 in the Byzantine calendar, or CE. The name of this future cathedral of Kiev probably commemorates Olga's baptism at Hagia Sophia.