21 Mayıs — Tarihte Bugün

Helena, mother of Constantine I

Christian feast day: Helena of Constantinople, also known as "Feast of the Holy Great Sovereigns Constantine and Helen, Equal-to-the-Apostles." (Eastern Orthodox Church, Anglican Communion)

Beatification

Christian feast day: Blessed Hemming of Turku

John Eliot (missionary)

Christian feast day: John Elliot (Episcopal Church)

Saints of the Cristero War

Christian feast day: Saints of the Cristero War, including Christopher Magallanes

May 21 (Eastern Orthodox liturgics)

Christian feast day: May 21 (Eastern Orthodox liturgics)

Circassian Day of Mourning

Circassian Day of Mourning (Circassians)

Armed Forces Day

Day of Patriots and Military (Hungary)

Independence Day (Montenegro)

Independence Day, celebrates the Montenegrin independence referendum in 2006, celebrated until the next day. (Montenegro)

International Tea Day

International Tea Day (International)

Navy Day (Chile)