The Druze are first mentioned in Season One “The Keys” when Cassie and Cole trace the photo of a plate with strange markings to a PhD academic Edward Garret. He explains that the symbols relate to an off-shoot of the Druze religion which exists in Chechnya.

The Druze Plate

Olivia also refers to the Druze in webisode 7 ‘Message’ where she is given the same plate seen in the photo in season 1:

“For a very long time we’ve admired and enlisted the help of the Druze Brotherhood.”

The Druze is a monotheistic religious group found primarily in Syria, Lebanon and Israel.

From Encyclopedia Britannica:

The Druze permit no conversion, either away from or to their religion. Marriage outside the Druze faith is rare and is strongly discouraged. Many Druze religious practices are kept secret, even from the community as a whole. Only an elite of initiates, known as uqqāl (“knowers”), participate fully in their religious services and have access to the secret teachings of the scriptures, Al-Ḥikmah al-Sharīfah.

One aspect of Druze religion relates specifically to time.

Pact of Time Custodian
The Pact of Time Custodian (Mithaq Walley El-Zaman) is considered the entrance to the Druze religion, and they believe that all Druze in their past lives have signed this Charter, and Druze believe that this Charter embodies with human souls after death. source: wikipedia.org

 

WARNING – Season 4 spoilers follow

In the later half of season 4 we are introduced to Andrus, a self-loathing Primary who is in league with the Witness. Andrus has established the seeds of a group known as the Brotherhood of Andrus across Europe and the Middle East. The name ‘Andrus’ seems to be the origins or possibly derived from the name ‘Druze’ within the show’s mythology.