Medieval Greek, also known as Byzantine Greek, is the stage of the Greek language between the beginning of the Middle Ages around 600 and the Ottoman conquest of the city of Constantinople in 1453. The latter date marked the end of the Middle Ages in Southeast Europe. From 620 onwards, Greek was the only language of administration and government in the Byzantine Empire, due to the reforms of Heraclius. This stage of language is thus described as Byzantine Greek. The study of the Medieval Greek language and literature is a branch of Byzantine Studies, or Byzantinology, the study of the history and culture of the Byzantine Empire.