On September 17, the feast day of the St. Sofia church, which gave the name to the city, was celebrated in the Bulgarian capital, Sofia. A representative from the Russian Orthodox Church participated in the festivities, as reported by the Synodal Department for External Church Relations.

The divine liturgy on this day was led by the vicars of the Sofia Metropolis, Bishop Polikarp of Belogradchik and Bishop Isaak of Velbuzhd, with the participation of Protopresbyter Vasilii (Savov), the protosynkellos of the Sofia Metropolis, representing the Patriarch of Moscow and All Russia at the Bulgarian Patriarchate, Archimandrite Vassian (Zmeev), the head of the Sofia Metropolis, Archimandrite Euthymius (Koinev), the rector of St. Sofia Church, Luchezar Popov, and the clergy of Sofia.

The ancient St. Sofia church was built in the 5th century in the ancient city of Serdica, present-day Sofia, and was dedicated to Hagia Sophia, the Wisdom of God. In the 6th century, under Emperor Justinian, it was rebuilt and renovated. In the 14th century, the Church of St. Sofia became the cathedral of the metropolitan bishop, giving the city its name. The church has stood for 1,700 years, hosting Orthodox services, although during the Turkish rule, it was briefly converted into a mosque. In the mid-19th century, the Ottomans repurposed it as the central firefighting service center for the city. In 1930, the church was placed under state protection as an architectural monument, undergoing several restorations during the 20th century. In 2013, the church's frescoes were restored and preserved, and an underground museum was constructed within the church.