History of the Peloponnesian War

The oracle also which had been given to the Lacedaemonians was now remembered by those who knew of it. When the God was asked whether they should go to war, he answered that if they put their might into it, victory would be theirs, and that he would himself be with them.

With this oracle events were supposed to tally. For the plague broke out so soon as the Peloponnesians invaded Attica, and never entering Peloponnese (not at least to an extent worth noticing), committed its worst ravages at Athens, and next to Athens, at the most populous of the other towns. Such was the history of the plague.