Dionysius the Phocaean or Dionysius of Phocaea was a Phocaean admiral of ancient Greece during the Persian Wars of 5th century BC, and was the commander of the Ionian fleet at the Battle of Lade in 494 BC. Although commanding a formidable force, according to the Greek historian Herodotus, his men were worked so hard in preparing for battle that on the eve of the battle they refused to engage the Persian fleet.