Put simply the Order of the Circles focuses are magic. All Advent mages belong to this Order, though not everyone in the Order of Circles is a mage. The Order of Circles performs three important tasks for the Advent. Firstly they provide much needed support for the other Orders in the form of magic. Most supernatural creatures and beings are more vulnerable to magic than to conventional weapons. Secondly they attempt to catalog and monitor all human mages, removing any threats they feel are necessary to protect humanity as a whole. Lastly they track down power artifacts and monitor places of power around the globe.
While most members of this Order are not active combatants, the mages of the Advent are quite capable of defending themselves and others. In addition most members have access to minor magical artifacts and gifts which make them a threat to any supernatural being or creature.
Like the Observants, the Moirai monitor Circle members carefully for any sign of corruption. Because of this Circle members are rarely given any role of authority within the Advent structure, being regulated to mostly supportive roles.