Slavs
Slavs can be further grouped by religion. Orthodox Christianity is practiced by the majority of Slavs. The Orthodox Slavs include the Belarusians, Bulgarians, Macedonians, Montenegrins, Russians, Serbs, and Ukrainians and are defined by Orthodox customs and Cyrillic script as well as their cultural connection to the Byzantine Empire (Serbs also use Latin script on equal terms). Their second most common religion is Roman Catholicism. The Catholic Slavs include Croats, Czechs, Kashubs, Moravians, Poles, Silesians, Slovaks, Slovenes, and Sorbs and are defined by their Latinate influence and heritage and connection to Western Europe. There are also substantial Protestant and Lutheran minorities especially amongst the West Slavs, such as the historical Bohemian (Czech) Hussites.
History of Proto-Slavic
Despite these developments, Slavic remained conservative and was still typologically very similar to other Balto-Slavic dialects. Even into the Common Era, the various Balto-Slavic dialects formed a dialect continuum stretching from the Vistula to the Don and Oka basins, and from the Baltic and upper Volga to southern Russia and northern Ukraine. Exactly when Slavs began to identify as a distinct ethno-cultural unit remains a subject of debate. For example, links the phenomenon to the Zarubinets culture 200 BC to AD 200, Vlodymyr Baran places Slavic ethnogenesis within the Chernyakov era, while Curta places it in the Danube basin in the sixth century CE. It is likely that linguistic affinity played an important role in defining group identity for the Slavs. The term "Slav" is proposed to be an autonym referring to "people who (use the words to) speak."