Pliny the Younger (A.D. 62?–c.A.D. 113). Letters.
The Harvard Classics. 1909–14.
XXXI. Trajan to Pliny
THERE is no occasion, my dearest Secundus, to draw off any soldiers in order to guard the prisons, Let us rather persevere in the ancient customs observed in this province, of employing the public slaves for that purpose; and the fidelity with which they shall execute their duty will depend much upon your care and strict discipline. It is greatly to be feared, as you observe, if the soldiers should be mixed with the public slaves, they will mutually trust to each other, and by that means grow so much the more negligent. But my principal objection is that as few soldiers as possible should be withdrawn from their standard.