On May 11, 1851, in Plovdiv, the Bulgarian writer and linguist Nayden Gerov officially organized the first holiday in honor of the holy brothers Cyril and Methodius.
The celebration took place in the diocesan school, named after the creators of the Glagolitic script.
The date was chosen because this was the common church holiday of the two saints. In the Bulgarian Renaissance sources, the first notices of the celebration of Cyril and Methodius on May 11 are found in the “Christomatiya slavyanskogo yazyka“ from 1852 by Neofit Rilski.
The Plovdiv Diocesan School, known as the First Men's Gymnasium, was also the first in the world named after the brothers Cyril and Methodius. The story of how it got its name is very interesting. "Dr. Stoyan Chomakov and I were gathered at the house of chorbadji Salcha Chomakov, and the question arose as to what name to give the school. I told him about what the holy brothers had done, and chorbadji Salcho was delighted with their work. So by common consent we named the school "St. Cyril and Methodius" and ordered an icon with the image of the saints. The holiday had to be celebrated. The school introduced this holiday, which has remained to be celebrated in the future. Following the example of the people of Plovdiv, many places in Bulgaria later began to name their schools after the two holy brothers," says Nayden Gerov in 1894 in his memoirs.
In 1856, Joakim Gruev proposed that the day of Cyril and Methodius be celebrated as a holiday for Bulgarian students. In 1857, the holiday was honored in the Bulgarian church "St. Stephen" in Constantinople, along with a service for St. Ivan Rilski. The following year, 1858, this day was also celebrated in Plovdiv with a solemn service in the church "St. Mary", and then the teacher Joakim Gruev delivered a moving speech about the life and work of Cyril and Methodius.
The Bulgarians themselves also initially considered it unusual to celebrate the day of the Holy Brothers and only in the fourth or fifth year of the first celebration did they begin to come for the celebrations. Subsequently, more and more people joined the celebrations, especially when Plovdiv acquired a Bulgarian church in 1860.
In the years that followed, May 11 began to be solemnly celebrated in the Bulgarian church "St. Stephen" in Constantinople, again in Plovdiv in the church of the “Holy Mother of God” (with a speech by Joakim Gruev), in Shumen, Lom, Skopje and Sofia. The holiday began to be regularly celebrated in Shumen and Lom, since 1860, in Skopje since 1862, in Varna since 1863.
After the introduction of the Gregorian calendar in 1916, the holiday was celebrated on May 24 according to the official state calendar, and according to the church liturgical calendar this day is dated May 11. In 1968, the Bulgarian Orthodox Church, already with the status of a patriarchate, introduced the so-called New Julian calendar as a liturgical calendar, through which the error of the old Julian calendar was eliminated. Thus, the day of Cyril and Methodius is honored by the Church on May 11 according to the church calendar. But due to the already established civil tradition, the secular, civil and state celebration remains on May 24, recalls the newspaper "Maritsa".
May 24 was declared an official holiday of the People's Republic of Bulgaria by a decision of the Ninth National Assembly on March 30, 1990, and since November 15, 1990 it has been an official holiday of the Republic of Bulgaria.