Clad in midnight blue, the Praeses Mercatura ultimately answer to the Speaker for the Chartist Captains and protect the Speaker's personal domain on Terra, known as the Nexus Axiomatic. The Mercatura's formation dates back to the aftermath of the Siege of Terra, where the Nexus was nearly destroyed before Horus' forces were defeated. To ensure that never happened again, the Speaker created the Mercatura and armed them with ancient weaponry and technology, to wield in the rebuilt Nexus' defense.
The Praeses Mercatura are a lightly armed force designed around protection and internal security, with its infantry wearing little armor and being armed with Lasguns and Laspistols. They also utilize gunships and Gun-Servitors.