Prætorian Guard, a select body of soldiers distributed in cohorts, as many as ten of a thousand each, to guard the person and maintain the power of the emperors, and who at length acquired such influence in the State as to elect and depose at will the emperors themselves, disposing at times of the imperial purple to the highest bidder, till they were in the end outnumbered and dispersed by Constantine in 312.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Prætor * Pragmatic Sanction