User blog comment:Suparockr/List of Plotholes throughout the series/@comment-24163193-20141103163437/@comment-24200891-20141103205107

Leviathans are colossal creatures, much less of them would be needed to built a Reaper. Harbinger is he very first reaper, but even it alone isn't invincible against a fleet, so Harbinger needed more of it's kind to commit those genocides and survive. It's unlikely Harbinger was alone during the first cycles, perhaps Souverign class ships are the reapers from the first cycle, but of course more of them appeared.