Perun's thunder and the last pagan holdout of Europe.
Slavic and Baltic paganism were the related pre-Christian religions of Eastern and Northeastern Europe, sharing an Indo-European inheritance of sky and thunder gods, animism, and ancestor veneration. Slavic tradition centered Perun, thunder god of law and war, honored beside Veles, ruler of livestock, wealth, and the underworld, with the pair representing complementary cosmic forces of sky and chthonic depth; Mokosh stood as the sole female deity in the official pantheon Prince Vladimir installed at Kyiv before his conversion. Baltic tradition, closely related linguistically, venerated Perkūnas (thunder), Dievas (sky), and Saulė (the sun goddess), with regional figures such as Lithuania's Gabija (fire) and Latvia's Māra appearing in local cult.
Ritual life centered on wooden temples and idols on hilltops for the Slavs, and sacred groves and shrines (alka) tended by priests called kriwe among the Balts. Volkhvs, Slavic priest-diviners, led seasonal festivals and banquets honoring ancestor-gods, while processions moved sunwise around sacred sites in both traditions. Neither culture left native written scripture; what is known comes almost entirely from outside witnesses — the Byzantine historian Procopius's sixth-century account of Slavic religion, German missionary chronicles describing Baltic grove-worship, and the Russian Primary Chronicle's description of Vladimir's pantheon before 988 — supplemented by later folklore and archaeology.
Christianization proceeded unevenly and slowly: South Slavs converted under Byzantine mission in the 860s–880s, East Slavs following Vladimir's baptism in 988, and West Slavic Poland from 966, intensifying through the twelfth-century Northern Crusades. The Baltic lands held out longest — Lithuania's official conversion in 1387 marked the last formal state-level paganism in Europe, with the process continuing into the sixteenth century in rural areas. In both regions, older practices persisted for generations alongside Christian observance in a pattern scholars call dvoeverie, or 'double faith,' leaving traces still visible in folk custom and seasonal festival today.
Slavic and Baltic paganism left no native scripture; what is known comes from outside accounts — the Russian Primary Chronicle's description of Perun's idols in Kyiv, and German missionary reports on Baltic grove-worship and priesthoods. Folk songs, festivals, and place names preserved fragments long after formal conversion.