Some things that are known about ancient Druids:

1. Holy days were on the solstices and equinoxes and mid-seasonal festivals (Halloween being the chief – New Year celebration.)
2. Animal and human sacrifices were practiced
3. Mistletoe, oak trees were used for sacred meetings

Since the druids originally came from the Celtic tribes. The Celtic tribes came to Europe from the holy land through the Caucuses Mountains. These are either the remnants of fleeing Persians, Assyrians, and/or ten tribes are reported in the Old Testament. Probably being a combination of all, each tribe will have slightly different parts of the pagan religions of Israel and elements of the patriarchal religion.

We are told in history that with the coming of the Christian church, some druids who practiced more of the patriarchal religion quickly became Christian, since they were already looking for the Messiah; this only left the corrupt pagan side that we are somewhat familiar with today.

If anyone knows of a written document for this religion please let us know. Since archeologists are constantly digging up new manuscripts one might surface someday.

Please send and information you have to manuscripts@biblefacts.org

Notes from other ancient sources:
In the Sonnini manuscript (Acts 29) there is a comment about one side of the druids tracing their linage back to the patriarchal religion before it was corrupted by the worship of Baal. When the apostle Paul was preaching in Brittan it says:

And it shall come to pass that certain of the Druids came to Paul privately, and showed by their rites and ceremonies they were descended from the Jews which escaped from bondage in the land of Egypt, and the apostle believed these things, and gave them the kiss of peace.

Pezron, in his Antiquities of Nations, pp. 93-94, says:
Zeus’ brother Dis, also called Pluto, was born near Dodona according to Strabo. Dis was called Agesander or Agesilaus by the Greeks. Dis lead a colony of Titians or Celtae into Spain and Gaul. The Druids of Gaul trace their descent back to him and his original settlement in Tartesa Spain.