Darius was the most influential Persion leader because he expanded the Persion Empire by sending his armies to conquer Thrace and Macedon as well as built huge temples and palaces throughout Persia. He was best known for his innovative building projects, The Royal Road, a massive canal, as well as a bridge of boats. Darius united the Persian empire and established a postal system. Religious tolerance was practiced under his rule. If it hadn't been for Darius the results of todays society would not exist.