21st May is the Feast Day of Constantine and Eleni.  The annual 'name day' celebrates Saint Constantine the Great and his mother Saint Eleni, who influenced the legalisation of Christianity in the colossal Roman Empire.  Constantine served with distinction under the Roman emperors Diocletian and Galerius, beginning his military career by campaigning in the eastern provinces against the Persians, before being recalled to the west in AD 305 to fight alongside his father and the 6th Legion in the province of Britannia, stationed at Eboracum (York) in Roman Britain.  Born in Naissus, a Roman province of Moesia (Serbia) Constantine became the emperor of the far Western Roman Empire upon the death of his father, Emperor Flavius Constantius I in AD 306, one of the four emperors of the Tetrarchy.

Constantine eventually emerged victorious in the civil wars against the emperors Maxentius and Licinius, to become the sole ruler of Rome and eventually the entire Roman Empire by AD 324.  He is venerated as a saint in Eastern Christianity and he did much to spread the Orthodox Christian religion towards the mainstream of Roman culture.  Although he lived most of his life as a pagan, he began to favour Christianity in AD 312, became a Christian himself, and was finally baptised before he died in Ancyrona, Bithynia.  Constantine the Great was buried at Constantinople in his Church of the Apostles, with the twelve memorials flanking his tomb.

Upon becoming sole emperor, Constantine soon recognised the shift of his new Roman Empire, from the remote and depopulated West to the richer and more prosperous cities of the East.  Among the various locations proposed for this alternative Roman capital, Constantine considered Serdica (Sofia) Sirmium and Thessalonica.  Eventually, Constantine decided to work on the Greek city of Byzantium, which offered the advantage of having already been rebuilt in Roman patterns of urbanism during the preceding century.  The imperial city was founded in AD 324, dedicated on 11th May AD 330 and renamed Constantinopolis, the 'City of Constantine'.  Since the throne of imperial rule was transferred to Constantinople from Rome, the inhabitants of its domain were called Romans (Romaioi) although most spoke Greek, and it was considered the continuation of the Roman Empire, evolving as a Christian state.  Saint Constantine the Great died on 21st May AD 337, aged 65, of which he ruled parts of and later the combined Roman Empire for 31 years. 

The name day for men celebrates Constantine, Constantinos, Costas or Kostas, Con, Connor, Tino, Dino and Dean.  'Xronia Polla!'

Eleni, Constantine's mother, was from a humble background, born in Drepanon, Bithynia, and is credited for the conversion of her son to Christianity.  After Constantine had made Christianity the main faith of the Roman Empire, Eleni undertook a personal pilgrimage to Jerusalem and found the Holy Cross on which Christ was crucified.  Eleni later erected churches in Jerusalem at the sites of the Crucifiction and Resurrection, in Bethlehem at the site where Christ was born, and yet another on the Mount of Olives.  She also established many other churches throughout the Holy Land and Cyprus.  Eleni/Helen was proclaimed 'Augusta' and her image was stamped upon golden coins while two cities in Bithynia and Palestine were named Helenopolis in commemoration of her.  Aghia Eleni (Saint Helen) died in Rome, aged 80, in AD 330. Saint Helen's (Flavia Julia Helena) individual feast day is celebrated on 1st August.

There are many different or shortened versions of Eleni, such as Helen, Helena, Helene, Elena, Elaine, Ellen, Lena, Eleanor, Eleonora, Nora, Marilena, also Nadia, Nandia, Thina, Tina, Dina for those christened Constantina, Konstandina or Constance.