There is no exhaustive or authoritative source that traces Wicca back through ancient times. Wicca is mainly a 20th century manifestation of ancient nature worship systems based out of northern Europe that existed thousands of years ago.
“Wicca is a religion rooted in the mists of Neolithic history . . . it is basically a fertility and agrarian society. It is a religion of nature worship and the subsequent interaction with nature that is dissented from that practice by the Celtic clans of Western Europe and the indigenous peoples of the British Isles, the builders of such monuments as Stonehenge.”1
“Wicca originated among the Celts and other peoples who lived in the area now known as Great Britain. Wiccans celebrate the Earth and believe all living things have a spirit. They espouse pantheism and claim to see the divine in everyone. Most celebrate monthly rituals, or "esbats," centered on the lunar cycles, and eight annual Wiccan holy days, or "sabbats," centered around the solar cycles, solstices and equinoxes.”2
These pagan oriented nature worship systems filtered down through history in countless ways but were mainly practiced in secret (and still are today). The secrecy was especially necessary during the European dominance of the Roman Catholic Church.
Basically, these pagan traditions developed out of agrarian societies where the environment had a profound effect upon survival. Those who studied the seasons and the stars sought to predict and understand the influences of the environment upon crops, cattle, rain, etc. and in so doing also desired to be able to influence these factors. It was from the desire to understand and control nature that gave rise to the various pagan and earth based worship systems. Therefore, we can see when we study ancient European pagan writings, there are countless deities.
Additionally, an important aspect of nature worship deals with the woman. It is the woman who was able to give birth to continue the race. In cultures where offspring were needed to work the land, to hunt, and to care for the elderly, women were, of course, vitally necessary. Therefore, the female became--in some cultures--mystically endowed with special powers, and this mystical endowment was transferred into the various theological pagan worship systems.
At first, there were a great number of cultures located all over the ancient European landscape. Since Europe is a large area and since weather patterns, terrain, water supplies, temperature variations, animal types, etc., varied in those areas, the development of nature worship (Druids, Celts) also took on aspects that reflected those variables. Therefore, the ancient systems could be polytheistic, monotheistic, feminine focused, masculine focused, ritualistic, calendar based, hunter based, etc.
Because of the multifaceted and buried background, the nature based worship systems were not codified, and there is no "official" pagan tradition. Nevertheless, today's Wicca is based upon these ancient and pagan roots.
Common Wiccan beliefs include:
Respect for nature - all living things are regarded as having or containing a spirit or an essence worth respecting. Wicca is widely regarded as an earth religion, very grounded in natural cycles, seasons and processes. Much of its ritual deal with bringing harmony and healing both to nature and to the self by becoming attuned to nature.
Gender Equality - Wiccans celebrate the sexual polarity in nature, and view the female as equal to the male. Some even view the female as superior in some respects, but in general male/female balance is an important concept in Wiccan belief.
Afterlife - Wiccans hold a wide variety of beliefs about afterlife. Some believe in ancient legends that speak of souls going to a place after death, reviewing their lives, and even being reborn into a new baby. Others envision themselves living on after death in nature via natural decomposition (in the soil or in other living beings). Also, some Wiccans envision an afterlife solely in terms of one's memory and influence in the lives of those left behind.