Tesserarii recruitment is a mystery to most, but the leading hypothesis is that a munifex who demonstrates exceptional loyalty to Caesar is approached with the offer to become a tesserarius. If the offer is accepted, it is with the understanding that the procedure to give the tesserarii their psychic powers destroys past memories, and the tesserarius's life prior to the procedure will be erased and can never be regained. Tesserarii must also agree to remain in service of the Fleet for the rest of their lives.
The mind-reading tesserarii are used officially as interrogators, both of enemies and of Imperians under suspicion of serious crimes. They are also tasked with reporting any suspected treachery against Caesar Immortalis, reporting regularly to the @prae, a tesserarius with the closest position to Caesar himself.
Unlike others of the immunes classes, tesserarii are not awarded the Equestrian class upon retirement, because tesserarii do not retire. Due to their recruitment process, they have no families to retire to, and they live out their lives in service to the Imperia.