The period from the early centuries AD to the end of the Common Slavic period around 1000 was a time of rapid change, concurrent with the explosive growth of the Slavic-speaking area. By the end of this period, most of the features of the modern Slavic languages had been established. The first historical documentation of the Slavic languages is found in isolated names and words in Greek documents starting in the 6th century, when Slavic-speaking tribes first came in contact with the Greek-speaking Byzantine Empire. The first continuous texts date from the late 9th century and were written in Old Church Slavonic—based on the Slavic dialect used in the region of Thessaloniki in Greek Macedonia—as part of the Christianization of the Slavs by Saints Cyril and Methodius and their followers. Because these texts were written during the Common Slavic period, the language they document is close to the ancestral Proto-Slavic language and is still presenting enough unity, therefore it is critically important to the linguistic reconstruction of Slavic-language history.
This article covers historical developments up through the end of the Common Slavic period. For later developments, see History of the Slavic languages.
Proto-Slavic is descended from Proto-Balto-Slavic (the ancestor of the Balto-Slavic languages). This language in turn is descended from Proto-Indo-European, the parent language of the vast majority of European languages (including English, German, Spanish, French, etc.). Proto-Slavic gradually evolved into the various Slavic languages during the latter half of the first millennium AD, concurrent with the explosive growth of the Slavic-speaking area. There is no scholarly consensus concerning either the number of stages involved in the development of the language (its periodization) or the terms used to describe them. For consistency and convenience, this article and the Proto-Slavic article adopt the following scheme:
Slavic scholars differ widely in both the terminology and periodization of these developments. Some scholars do not use the term "Common Slavic" at all. For some others, the Common Slavic period comes after Proto-Slavic rather than including it. Some scholars (e.g. Frederik Kortlandt) divide the Common Slavic period into five or more stages, while others use as few as two (an early, uniform stage and a late, dialectally differentiated stage).
The currently most favoured model, the Kurgan hypothesis, places the Urheimat of the Proto-Indo-European people in the Pontic steppe, represented archaeologically by the 5th millennium BCE Sredny Stog culture. From here, various daughter dialects dispersed radially in several waves between c. 4400 and 3000 BC. The phonological changes which set Balto-Slavic apart from other Indo-European languages probably lasted from c. 3000 to 1000 BC, a period known as common Proto-Balto-Slavic. Kortlandt (1990) links the earliest stages of Balto-Slavic development with the Middle Dnieper culture which connects the Corded Ware and Yamna cultures. Kurganists connect the latter two cultures with the so-called "Northwest (IE) group" and the Iranian-speaking steppe nomads, respectively. This fits with the linguistic evidence in that Balto-Slavic appears to have had close contacts with Indo-Iranian and Proto-Germanic.