Holy Cross Day, or the Feast of the Exaltation of the Holy Cross, is a Christian festival celebrated on 14 September. Those Eastern churches that use the Julian calendar celebrate on the same date in that calendar, which is currently 27 September in the Gregorian calendar.
The festival commemorates the finding in Jerusalem of the Cross on which Jesus died, by Saint Helena, the mother of Emperor Constantine, in 326. This was during a period of renovation of the traditional place of the crucifixion and the building of the Church of the Holy Sepulchre by Macarius, Bishop of Jerusalem, under the instruction of Constantine. The earliest account of this is given in the Ecclesiastical History of Socrates Scholasticus (b. 380). This account was later expanded by Sozomen and Theoderet of Cyrrhus. Of these, Theodoret's account has become the standard.
All the accounts describe the demolition of the pagan Roman temple that had been built on the site, and the discovery of the three crosses (for Jesus and the two thieves who were crucified with him) buried near the tomb. The accounts say that Bishop Macarius resolved to discover which of the three crosses was the true Cross of Christ, and he had each in turn laid upon a noble lady of Jerusalem who was suffering from an incurable disease. The third cross to be placed upon her cured her of her disease instantly, and was thus deemed to be that of Christ.
The celebration of the exaltation, or lifting up, of the Cross is more popular in Eastern Christian churches than it is in the West. Many Eastern Churches hold processions and light bonfires in high places to celebrate the day. The lighting of bonfires is supposedly connected to the beacon fires ordered by Helena to relay the joyful news to Constantinople.