When in history...

[Watchman]

"Empire" is pretty much a relationship anyway - one of power, to be more specific. The word only really has real meaning in the context of multiple actors; the ones with sufficient clout, influence, standing etc. are "empires". You could say that whoever is regarded as a big shot and someone to pay close attention to by a sufficient (rather arbitrary) portion of the communities and other political actors of its relevant time and place qualifies. Eg. the Genoan and Venetian mercantile empires (which actually kinda remind you of Carthage at its heyday), Sweden in its Great Power period (which incidentally ended at Poltava in 1712)... move to a point of time when they're not that powerful and influential, and they're just another bunch of tossers. Kinda like how Rome only starts counting as an empire when it first becomes a major player in its reference area, or Byzantium was an Empire in name only (literally enough) in the period just before the Ottomans mopped up the last vestiges.

This isn't the same thing as the existence of a civilization, community etc. as a distinct entity, except of course it's sort of hard to be an empire if you don't exist anymore - but per definition any such actor that disappears in such a fashion has to have lost the imperial status at somepoint beforehand, anyway. Unsurprisingly most such entities were in existence far longer than they could be counted as empires; eg. Babylon was an empire on at least two occasions, but the city itself existed for a far longer period without being powerful and influential enough to make the cut.

And of course calling yourself an Empire in some permutation doesn't make you an empire, anymore than calling your state People's Democratic Republic makes it a democracy. The HRE is a sort of good case in point. The Hansa merchant cities and the Teutonic Order's Ordensstaat were most of the time by far closer to that status (albeit only in the Baltic, obviously) than that nigh-unmanageable mess.