In the Christian liturgical calendar, there are several different Feasts of the Cross, all of which commemorate the cross used in the crucifixion of Jesus.
In English, it is called The Exaltation of the Holy Cross in the official translation of the Roman Missal, while the 1973 translation called it The Triumph of the Cross. In some parts of the Anglican Communion the feast is called Holy Cross Day, a name also used by Lutherans.
The Feast of the Exaltation of the Holy Cross, recalls three events: the finding of the True Cross by Saint Helena, the mother of the emperor Constantine; the dedication of churches built by Constantine on the site of the Holy Sepulchre and Mount Calvary; and the restoration of the True Cross to Jerusalem in AD 629 by the emperor Heraclius after it had fallen into the hands of Chosroas, King of the Persians in AD 614.
September 16 is observed as the Feast of the Exaltation of the Holy Cross, a feast which continues for several days thereafter. It is counted as one of the five major feasts of the Armenian Church, and the most important of the four feasts of the Holy Cross. According to Armenian tradition, the first one to “exalt” the Cross was the Apostle James of Jerusalem, the “Brother of the Lord”.
Here are Mehr’s photos of the feast celebrated in the Holy Cross Chapel in northern Tehran: