The principles of military strategy emerged at least as far back as 500 BC in the works of Sun Tzu and Chanakya. The campaigns of Alexander the Great, Chandragupta Maurya, Hannibal, Qin Shi Huang, Julius Cæsar, Zhuge Liang, Khalid ibn al-Walid and, in particular, Cyrus the Great demonstrate strategic planning and movement. Mahan describes in the preface to "The Influence of Sea Power upon History" how the Romans used their sea power to effectively block the sea lines of communication of Hannibal with Carthage; and so via a maritime strategy achieved Hannibal's removal from Italy, despite never beating him there with their legions.