Point of Divergence:
Breaking News - An ancient shipwreck was discovered recently off the coast of Cyprus. Archaeologists believe that the ship was Egyptian in origin, dating from somewhere in the 400s or 300s B.C. Inside, they found the miraculously preserved journal of a crew member. Here is the translation of the last entry:
We left Sidon not two days ago with fresh supplies. A storm has come to our ship. We pray each day for deliverance, but none has come. Two more men have become ill, with what we don't know.
Scientists have also found microbes of Yersiana Pestis in the boat.
In OTL, an Egyptian merchant ship believed to be from Pelusium sailed to Athens. This ship is presumably caused an outbreak of plague, costing Athens almost two-thirds of its army and its dynamic leader, Pericles. Not long after, Spartan armies broke through into Athens, ending its golden age. Here, however, that ship sank and allowed Athens to fight the Spartans.