Classical civilizations and later cultures had much influence on the Balts' culture, but they did not succeed in changing their beliefs. For the Baltic tribes, their ancient religion was not only the foundation of their worldview, but also the source of strength needed to battle against Christian Crusaders and other invaders. Lithuania was the last pagan state in Europe; the acceptance of Christianity began only 600 years ago after two attempts. Zemaitija, the western region of Lithuania, only began its religious conversion in 1413.
Ancient Baltic religion can be roughly reconstructed from historical sources and from customs and folklore still in use today. It retained many of the main polytheistic elements of ancient Indo-European religions including a three-tiered world structure. It is thought that at the top of the Baltic pantheon stood Dievas (God) who lived in the sky. Under him was the most active and powerful mythological personage, Perkunas, god of thunder. Perkunas was endlessly engaged in battle with his enemy, Velnias, who ruled the underworld. Teliavelis, the blacksmith god who crafted the sun and set it in the sky, assisted Perkunas. The sun, moon, morning star and the stars comprised the heavenly family which took part in a mythological wedding. Even today, one can still find the roofs of houses decorated with zirgeliai (pairs of wooden carvings in the form of steeds' heads) which are relicts of the cult of the twins.
There also existed a great number of lesser deities who were associated with agricultural labor cycles and who directed various aspects of nature and everyday life. The initiators of various mythological traditions were also deified. The numerous female deities (especially common in Latvian mythology) most likely survived from pre-Indo-European times. Many spirits lacking individual identities, and usually human forms, are still believed in today.
The outlooks of the various Baltic tribes differed somewhat, and they further altered as time passed. This division was reflected through the variety of burial customs which included the use of burial mounds, cremation, sinking and other methods. The dead were accompanied into the next world by their work tools, weapons and often steeds which the Balts held in great esteem.
Baltic sorcerers conducted religious ceremonies in sacred oak groves and on hills called alkai where holy fires were built within altars. One of the centers of religious activity was located in Vilnius in the Sventaragis vale where the cathedral stands today. The central Prussian temple, called Romove, was as sacred to Prussian and most likely other Baltic tribes as Rome is to Catholics.