Name Days, not birthdays, are celebrated in Greece. Great significance is attached to the name given a child, and the process of choosing a name follows fairly rigid conventions. The idea of a baby being given a name just because the parents like the sound of it is unknown in Greece. Even naming a child after someone as a mark of respect or admiration is unusual.
Naming conventions in Greece are still followed quite strictly, with the result that certain names are used for many individuals in a generation. In each generation, the eldest grandson in each family will be named for the grandfather, and the eldest granddaughter will be named for the grandmother. If someone had three children, and they all produce a male grandchild, all three of those cousins will have the same name. To top it all off, all those with the same first name will celebrate the same saint's Name Day. Names are usually of religious origin.
Each saint has a special feast day. A person's name day is the feast day of the saint after which they were named. On someone's name day, open house is held and a feast is laid on for the friends and neighbors who call. They will give a small gift to the person whose names day it is, but there is less emphasis on the giving of presents than there is in birthday celebrations. (taken from: http://www.symivisitor.com/greek_name_days.htm)
St. Constantine (the Great)
(d. 337)
The son of St. Helen, who became emperor when his father Constantine Chlorus died in 306 after having defeated his rival Maxentius at the battle of the Milvian bridge.After having seen a vision of a cross in the sky, St. Constantine became Christian, according to legend, but was not baptized until his deathbed.
St. Constantine was very much involved in the church's affairs, and presided in councils, had churches built and made legislations based on Christian beliefs and morals. In the East he his often called the "13th apostle".
On his and his mother's nameday, the tradition of walking across burning is coal is still a custom in northern Greece.
Orthodox nameday: 21/5