THE SLAVS AND THE SLAVIC MYTHOLOGY.

Slavs are the largest Indo-European group in Europe. They inhabit Central Europe, Eastern Europe, SouthEast Europe, North Asia, and Central Asia. Presently over half of Europe's territory is inhabited by Slavic-speaking communities. Slavs speak Indo-European Slavic languages and share, to varying degrees, some cultural traits and historical backgrounds. They are classified as West Slavic (Poles, Czechs, and Slovaks), East Slavic (Russians, Bela-Russians, and Ukranians), South Slavic (Serbs, Bulgarians, Croats, Bosniaks, Macedonians, Slovenes, and Montenegrins), though sometimes the West Slavs and the East Slavs are combined into a single group known as North Slavs.
The meaning of the word "Slav" in the Old Slavic denotes "people who speak the same language," in contrast to the modern meaning as "foreign people" or as "mumbling, murmuring people."
From the early 6th century they spread to inhabit most of Central and Eastern Europe and SouthEast Europe, while Slavic Mercenaries fighting for the Byzantine and Arabs settled Asia Minor as far as Syria. The East Slavs colonized Siberia and Central Asia.
Slavic mythology is the religion practiced by the Slavs before Christianisation. Old Slavic religion evolved for a 1000 years and some part of it from 10,000 to 12,000 BC. All their original religious beliefs and traditions were passed down orally over the generations. An exception is a short note in Herodotus' Histoires, mentioning the Tribes of Bhudini and Neuri in the far North, whose men, supposedly transform themselves into wolves for several days each year.
The Bhudini (Greek: Boudino) were a large and numerous ancient people who lived in Scythia. Above the SarmaTians, possessing the Second Region, dwelt the Bhudini, whose territory was thickly wooded and planted with trees of all manner of kinds. In the very woodiest part was a broad deep Lake, surrounded by marshy ground with reeds growing on it. Otters were caught, and beavers, with another sort of animal which had a square face. With the skins of this last the aboriginals bordered their capotes. Also they got from them a remedy, which was a virtue in diseases of the womb. Beyond the Bhudini, going NorthWard, first there was a Desert, 7 days' journey across the land. Herodotus located them East of the Don River (Tan-Ais in his time), one of the major Rivers of Russia that flows for a distance of about 1950 km /1220mi to the Sea of Azov,  beyond the Sarma-Tians, a large confederation of Iranian people that flourished from about the 5th BC to the 4th century CE.
Herodotus also made a description of the Bhudini, East of the Danube (Ister) River, thusly. A large, numerous and powerful nation where all had a "mighty deep blue eyes," and "bright red hair." A City-Town among them was built by a different kind of race. The Town was made of wood and was  named Gelonus and was made the capital city of the Scythian Tribe of the Bhudini. The Gelonii were formerly Greeks, having settled away from the coastal emporia among the Bhudini, where they "used a tongue partly Scythian and partly Greek."
The Bhudini, however, did not speak the same language as the Gelonii, nor was their mode of life the same. They were the aboriginal people of the land, and were nomads. Their food was different that the ones of the neighboring races.
The Gelonii became increasingly settled and wealthy on their Western Frontier with Greco-Roman Civilization. Each side of its high outer Wall was 30 stades long (about 30 square km), entirely of wood, and its houses were also made of Wood. There were in every place Greek gods' shrines adorned in the Greek way with statues, altars and wooden shrines. Every 3rd Year they celebrated a Festival of DionYsus and became possessed by the god.
The fortified Wooden Settlement of Gelonus was reached by the Persian Army of Darius in his assault of Scythia (6th century BC), already burned to the ground, having been abandoned it before the persian advance. they sent a message to Darius:"We are as free as Wind and what you can catch in our ground is only the Wind." By employing a scorched earth strategy, they avoided battles, leaving "earth without grass" by burning the steppe in front of the advancing Army. The Persian Army returned without a single battle or any significant success. The city was strategically situated on the exact boundary between the steppe and forest-steppe.
The archaeological site around Belsk, including necropolis, comprises about 80 km2, and the fortifications enclose some 40 km2. The North-South axis, along the Vorskla River is 17 km long. The remains of walls up to 12 metres are visible today and stretch over the horizon. The total length of the ramparts is 33kms. Inside the fortification, lay 3 "keeps," 150,000m2, 650,000m2, and 720,000m2 in area, surrounded by eroded earth Walls still up to 16 meters high. Several burial mounds reminded the inhabitants of the ancient Scythian burial tradition.
In Greek mythology, Gelonus was the son of Echidna and Heracles. He had an older brother AgathYrsus and a younger Scythes. Hylea is pointed to be where the Echidna's Cave was between the people. The Greeks believed that this was somewhere in Scythia.
The first Christian conversion group began in Bulgaria in 864 CE and was largely complete by the late 11th century.
Unlike ancient Greek, Indian (Hindu), Chinese or Egyptian mythology, there are no first-hand records of it. Archaeological remains of Old Slavic cult images and shrines have been found, though little can be  yielded from them without legitimate knowledge of their contexts. Fragments of the old beliefs and festivals survive up to this day in folk customs, songs, and stories.