User blog comment:The Milkman/No Love For Leviathan?/@comment-4947725-20120918053701/@comment-2228120-20120918060151

Didn't it say that the Catalyst created synthetic servants to help it carry out its research into the synthetics vs organics problem, and then turned these servants against the Leviathans? Synthetics most probably couldn't be controlled by the Leviathans, and without the aid of their organic slaves, they would really be helpless, especially when taken by surprise. Besides, there were no Reapers yet at that time, since the first one, Harbinger, was made only from the Leviathans themselves.