Upvote:2
Tacitus Agricola 29-32 on Calgacus's speech to his army of Britions/Caladonians where Calgacus referred to the (Roman) empire. "Robbers of the world, having by their universal plunder exhausted the land, they rifle the deep. If the enemy be rich, they are rapacious; if he be poor, they lust for dominion; neither the east nor the west has been able to satisfy them. Alone among men they covet with equal eagerness poverty and riches. To robbery, slaughter, plunder, they give the lying name of empire; they make a solitude and call it peace (ubi solitudinem faciunt, pacem appellant).
Also
Rome was used to refer to the roman state, not just the city. Coins were stamped with Roma.
Also these terms came into us after the first republic was established and SPQR appeared on documents.