Mediterranean hegemon

It was an era of the rise of the greats: the vast Persia, the Sparta which was founded on martial arts, the Athens which dominated in trade and commerce, the Thebes which was a rising star, the ambitious Macedonian, the twin heroes of the Western Mediterranean, and the newly-emerged Rome. ......
It was an era of brilliant generals: Agesilaus, the last king of Sparta, Epaminonda, the famous general of Thebes, Philip, the founding king of Macedonia, Dionysius, the tyrant of Syracuse, and Camillus, the dictator who saved Rome ......
It was a time of a hundred schools of thought: Plato, the great philosopher; Antisthenes, the founder of Cynicism; Pythagoras, who made number his god; Democritus, the encyclopedic scholar; Hippocrates, the father of Western medicine; Aristophanes, the great dramatist ......
The protagonist crosses over and is reborn as a lowly mercenary in this era, what will he bring to the world?