Meskel, in the Ethiopian Orthodox Church, is an annual religious holiday commemorating the discovery of the True Cross by Queen Helena (Saint Helena) in the fourth century. Meskel occurs on 17 Meskerem in the Ethiopian calendar (September 27, Gregorian calendar, or September 28 in leap years). The word "Meskel" is Ge'ez for "cross".
The festival is known as Feast of the exaltation of the holy cross in other Orthodox, Catholic or Protestant churches. The churches that follow the Gregorian calendar celebrate the feast on September 14. One explanation for the high rank this festival has in the church calendar is that it's believed that a part of the true Cross has been brought to Ethiopia from Egypt. It is said to be kept at Amba Geshen, which itself has a cross shape.
The Meskel celebration includes the burning of a large bonfire, or Demera, based on the belief that Queen Eleni had a revelation in a dream. She was told that she shall make a bonfire and that the smoke would show her where the true cross was buried. So she ordered the people of Jerusalem to bring wood and make a huge pile. After adding frankincense to it the bonfire was lit and the smoke raised high up to the sky and returned to the ground, exactly to the spot where the Cross had been buried.