Ethiopian calendar in the context of "Tekle Haymanot"

The Feast of the Holy Cross, Feast of the Exaltation of the Holy Cross, or Feast of the Cross, commemorates the True Cross. On 13 September, 335, the Constantinian Basilica over the Holy Sepulchre was consecrated in Jerusalem. The day after the church's consecration, the relic of the cross was shown ("exalted") for the first time to the people for veneration. Later, the feast was also associated with the commemoration of the recovery of the Holy Cross by emperor Heraclius on 13 September 628.

In the liturgical year, there are several celebrations which honor and celebrate the cross used in the crucifixion. Unlike Good Friday, which is dedicated to the passion of Christ and the crucifixion, these feast days celebrate the Cross itself, as the sign of salvation. It is celebrated by Catholics (Latin Church Catholics, Eastern Catholics), Eastern Orthodox, Oriental Orthodox, Church of the East, Old Catholics, Lutherans and Anglicans, and to a lesser extent by Presbyterians, Methodists and Baptists. The most common day of commemoration is September 14 for churches that use the Gregorian calendar and September 27 for churches that use the Julian calendar, Ge'ez calendar, or Coptic calendar.

The intercalary month or epagomenal days of the ancient Egyptian, Coptic, and Ethiopian calendars are a period of five days in common years and six days in leap years in addition to those calendars' 12 standard months, sometimes reckoned as their thirteenth month. They originated as a periodic measure to ensure that the heliacal rising of Sirius would occur in the 12th month of the Egyptian lunar calendar but became a regular feature of the civil calendar and its descendants. Coptic and Ethiopian leap days occur in the year preceding Julian and Gregorian leap years.

Mesori (Coptic: Ⲙⲉⲥⲱⲣⲓ, Masōri) is the twelfth month of the ancient Egyptian and Coptic calendars.

It is identical to Nahase (Amharic: ነሐሴ, Nähase) in the Ethiopian calendar.