The Byzantine Empire used a calendar that counted from the date of Creation of the World. This was calculated to be 1 September 5509 BC. Consequently, the Year of the World (called Etmos Kosmou in Greek) ran from 1 September to 31 August on the Gregorian Calendar.

Etos Kosmou in Agent of Byzantium[]

While being devout Christians, Eastern Romans did not favor calculating years from the time of the Incarnation, as was common in the Western Empire and continued by the Franco-Saxons. It instead used the Etos Kosmou dating system. Basil Argyros, when assigned to missions in this part of the world felt annoyed with the need to convert from one calendar to another, and regarded the Western calendar as rather barbarous.

Etos Kosmou in "The Emperor's Return"[]

The Byzantine Empire continued to use the Etos Kosmou system of dating until the fall of Constantinople to the Ottoman Empire on 29 May 1453 (Etos Kosmou 6961) resulted in the Empire's collapse.

As the Ottomans overran Constantinople, the last Byzantine Emperor Constantine XI Palaiologos entered the Hagia Sophia and asked for a miracle: to let God see the city in Christian hands again. With that, a mantle of flame bathed the emperor, and he sank into the marble floor before the eyes of the startled priest. Constantine returned on 10 June 2003 (Etos Kosmou 7511), shortly after Istanbul was overrun by the forces of Greece and the Soviet Union and the city once again fell under Christian control.