govern was obvious. Military achievements For more than 20 years Pericles led many expeditions, mainly naval ones. Being always cautious, he never undertook of his own accord a battle involving much uncertainty and peril and he did not accede to the "vain impulses of the citizens". He based his military policy on Themistocles' principle that Athens' predominance depends on its superior naval power and believed that the Peloponnesians were near-invincible on land. Pericles also tried to minimize the advantages of Sparta by rebuilding the walls of Athens, which, it has been suggested, radically altered the use of force in Greek international relations. During the Peloponnesian War, Pericles initiated a defensive "grand strategy" whose aim was the exhaustion of the enemy and the preservation of the status quo. According to Platias and Koliopoulos, Athens as the strongest party did not have to beat Sparta in military terms and "chose to foil the Spartan plan for victory". The two basic principles of the "Periclean Grand Strategy" were the rejection of appeasement (in accordance with which he urged the Athenians not to revoke the Megarian Decree) and the avoidance of overextension. According to Kagan, Pericles' vehement insistence that there should be no diversionary expeditions may well have resulted from the bitter memory of the Egyptian campaign, which he had allegedly supported. His strategy is said to have been "inherently unpopular", but Pericles managed to persuade the Athenian public to follow it. It is for that reason that Hans Delbrück called him one of the greatest statesmen and military leaders in history. Although his countrymen engaged in several aggressive actions soon after his death, Platias and Koliopoulos argue that the Athenians remained true to the larger Periclean strategy of seeking to preserve, not expand, the empire, and did not depart from it until the Sicilian Expedition. For his part, Ben X. de Wet concludes his strategy would have succeeded had he lived longer. Critics of Pericles' strategy, however, have been just as numerous as its supporters. A common criticism is that Pericles was always a better politician and orator than strategist. Donald Kagan called the Periclean strategy "a form of wishful thinking that failed", Barry S. Strauss and Josiah Ober have stated that "as strategist he was a failure and deserves a share of the blame for Athens' great defeat", and Victor Davis Hanson believes that Pericles had not worked out a clear strategy