Vidovdan, celebrating St. Vitus and an important day in Serbian history. (Eastern Orthodox Church)

Vidovdan is a Serbian national and religious holiday, a slava celebrated on 28 June, or 15 June according to the Julian calendar. The Serbian Church designates it as the memorial day to Saint Prince Lazar and the Serbian holy martyrs who fell during the Battle of Kosovo against the Ottoman Empire on 15 June 1389. It is an important part of Serb ethnic and Serbian national identity.

Vitus, whose name is sometimes rendered Guy or Guido, was a Christian martyr from Sicily. His surviving hagiography is pure legend. The dates of his actual life are unknown. He has long been tied to the Sicilian martyrs Modestus and Crescentia but in the earliest sources it is clear that these were originally different traditions that later became combined. The figures of Modestus and Crescentia are probably fictitious.

The Eastern Orthodox Church, officially the Orthodox Catholic Church, and also called the Greek Orthodox Church or simply the Orthodox Church, is one of the three major doctrinal and jurisdictional groups of Christianity, with approximately 230 million baptised members. It operates as a communion of autocephalous churches, each governed by its bishops via local synods. The church has no central doctrinal or governmental authority analogous to the pope of the Catholic Church. Nevertheless, the Ecumenical Patriarch of Constantinople is recognised by them as primus inter pares, a title held by the patriarch of Rome prior to 1054. As one of the oldest surviving religious institutions in the world, the Eastern Orthodox Church has played an especially prominent role in the history and culture of Eastern and Southeastern Europe. Since 2018, there has been an ongoing schism between Constantinople and Moscow, with the two not in full communion with each other.