In the early days of the founding of Hallifax, the Matrix was not a very well understood source of power and produced several temporal anomalies. The Holy Celestine Empire charged Hallifax with overseeing these anomalies, which sometimes released hostile entities through unstable dimensional rifts. At first, Hallifax employed mercenary companies to help investigate these anomalies, one of which was the Skylark Company of trill mercenaries. Hallifax eventually purchased exclusive rights to the employment of the Skylark Company and, together with Hallifax's temporal mechanics and engineers, founded the Sentinel Company of Temporal Anomalies (commonly called the Time Sentinels). Though eventually the Matrix stabilized, the Sentinels continued their initial mandate of monitoring the timestream, where they closely worked with the Matrix Institute. However, their duties eventually grew to encompass more traditional home guard and military assignments, especially in relation to procuring mining areas. This eventually led to the establishment of the Ministry of Peace, the bureaucratic branch which oversees the Sentinels. Today, the Sentinels operate as a highly ceremonial guard in the city of Hallifax, where their blue-white dress uniforms, silver breastplates and ornate halberds have become part of the culture of the city. The Company is a highly structured and rigid organisation, and those who seek to serve as Senior Officers generally must still have a degree in temporal mechanics.

Sentinels are a warrior archetype. Thus, they take Knighthood as their primary skill, though they may specialise upon reaching mastery as a Blademaster, Bonecrusher, Pureblade, Axelord, or Cavalier. Like all warriors, they take Athletics as a secondary skill. They also may take Rituals as a secondary skill, and can specialize in Aeonics. Alternatively instead of Rituals, they may choose Hunting and specialize in Tracking.