The dangers to the state from a "touch" from "without"

As in a body which is diseased, the addition of a touch from without may bring on illness, and sometimes even when there is no external provocation a commotion may arise within - in the same way wherever there is weakness in the State there is also likely to be illness, of which the occasions may be very slight, the one party introducing from without their oligarchical, the other their democratical allies, and then the State falls sick, and is at war with herself, and may be at times distracted, even when there is no external cause. Plato. The Republic. Book 8.

Grand Ludovisi Battle Sarcophagus depicting Roman conquest of Barbarians 2nd - 3rd century CE.
Photographed at the Palazzo Altemps in Rome, Italy.