This holiday is Greece's National Day and is always celebrated on 25 March.
Greece's Independence Day is actually a holiday that has blended over time with an older festival - the Feast of the Annunciation
In 1821, the Greeks rose up against the Ottoman Empire which had occupied Greece for almost 400 years, leading to the war of independence.
Bishop Germanos of Patras raised the Greek flag at the monastery of Agia Lavras, inciting the Peloponnese to rise against the oppressors.
While the exact date probably may not have been 25 March, it is acknowledged to have occured in late March and it was gradually associated with the religious feast of the Annunciation.
On this day in the Orthodox calendar, the archangel Gabriel appeared to the maiden Mary and informed her that she was pregnant with the divine child.
Greek Independence Day is also celebrated by many Greeks overseas, and large parades are becoming more common in United States cities where Greeks have made their homes, including Boston and New York City.
Each year, the U.S. President marks the occasion with a proclamation reminding citizens of the contributions of Greece to democracy, and of the ongoing contributions of expatriate Greeks in their new communities throughout the world.