Centurions are considered legendary warriors with their superior training. They are also scholars who, with their access to the elusive libraries of the Spiral Labyrinth and the Silent Brothers' archives, conduct research.
One of the Centurions' primary duty that distinguishes them from other Shadowhunters is that they investigate cases that do not fall under their Law and mandate. This includes dealing with and policing faeries in the advent of the Cold Peace. Before it was closed down after the signing of the First Accords, they dealt with demons and matters relating to Downworlders in general. Centurions report and answer directly to the Scholomance and the Council. They have vows that require them to tell the truth to the Clave and its officials.
Most, if not all, Centurions are those that graduated from the Shadowhunter Academy. Before getting admitted into the Scholomance, the Centurions had to pass a series of harsh tests. They are forbidden from sharing any of the information they learn from the school.
The uniform of Centurions is regular Shadowhunter gear and a military-style jacket, with metal buttons, sashed crossways with a pattern of vine staffs, and the Centurion's family crest on the back. The Centurions have a medallion or pin that signifies their status; the pin has a pattern of a leafless stick and the words Primi Ordines on it.
As of 2012, only a few years after the Scholomance was reopened, there were still only a few Centurions.
- Centurions are apparently not allowed to have parabatai.
- The youngest known aspirant to ever become a Centurion is Diego Rosales, who is also considered one of the best.
- An early draft of Lady Midnight states that Centurions are considered the most elite Shadowhunters who graduated with high honors from the Academy, and that some of the students who attended the Scholomance go on to become heads of Institutes.