Commemoration of religious figures and historical biographical data

On May 21, the Greek Orthodox Church commemorates Saints Constantine and Helena. Historical accounts regarding Constantine the Great's birthplace vary, suggesting locations such as Tarsus in Cilicia, Drepana in Bithynia, or Naissus in Moesia Superior, with the latter being the most accepted theory. His birth is estimated between 272 and 288 AD. Constantine's father was Constantius Chlorus, a relative of Emperor Claudius, and his mother was Helena. In 305 AD, Constantine served as a chiliarch in Nicomedia before Constantius Chlorus and Galerius were promoted to the rank of Augustus following the resignation of Diocletian and Maximian. Following his father's death on July 25, 306 AD, the army proclaimed Constantine as Augustus, a claim initially rejected by Galerius. Additionally, May 20 marked the commemoration of Saint Thallelaios and Saint Lydia of Philippi, who is considered the first Christian convert in Macedonia, baptized by the Apostle Paul in the Zygaktos River.