Bulgarians honor Saints Constantine and Helena, who are venerated as the Equals of the Apostles. Like the Apostles, they dedicated themselves to spreading the teachings of Christ. Saint Constantine, the founder and first emperor of the Byzantine Empire in the 4th century, made Christianity the official religion in Byzantium. His mother, Helena, discovered the cross on which Christ was crucified and built several monasteries in the Holy Land. This discovery is considered a pivotal event in Christian history, leading to their canonization as saints. According to the Bulgarian Patriarchate, St. Constantine's care for the Church before his baptism adds to his merit.

In Bulgaria, the day of Saints Constantine and Helena is marked by Nestinari dances on embers, blending Christian and pagan traditions. The Church honors them on May 21, which is also celebrated as the transition from spring to summer. People named Constantine, Kostadin, Konstantina, Elena, Eleonora, and Elitsa celebrate their name day. The name Elena, of ancient Greek origin, means "bright as the sun, radiant," while Constantine, from Latin, means "constant."

Saint Constantine, emperor of Byzantium in the 4th century, issued the Edict of Milan in 313 with co-emperor Licinius, ensuring tolerance towards Christians. Though Emperor Theodosius officially declared Christianity the state religion in 380, Constantine is considered the first Christian emperor of Rome. Despite being baptized only on his deathbed in 337, Constantine supported Christianity and called himself "foreign minister of the Church."

Helena, Constantine's mother, built several monasteries in the Holy Land and discovered the cross on which Jesus was crucified, a significant event in Christian history. For this, Constantine and Helena were canonized.

Today, the Bulgarian Orthodox Church celebrates with Divine Holy Liturgy in all churches. The day also marks chimney making and bonfires in Strandzha, where people gather around embers, carrying icons of Saints Constantine and Helena, and perform ritual dances. The cities of Elena and Pazardzhik also celebrate their holidays today.