In this ethnically diverse closing area of the Roman Empire, Vlachs were recognized as those who spoke Latin, the official language of the Byzantine Empire used only in official documents, until the 6th century when it was changed to the more popular Greek. These original Vlachs probably consisted of a variety of ethnic groups (most notably Thracians, Dacians, Illyrians) who shared the commonality of having been assimilated in language and culture of the Roman Empire with the Roman colonists settled in their areas. Anna Comnene relates in Alexiade about Dacians (instead of Vlachs) from Balkans and from the North side of Danube and they were identified as Romanians.[20] Romance-speaking populations survived on the Adriatic, and the Albanians are believed by some to be descending from partially Romanized Illyrians.