This thesis explores why the Athenians designed and erected the particular defensive infrastructure that they did, the Themistoclean circuit walls and, in particular, the Long Walls. These fortifications were completed at various stages during the Pentekontaetia (479-431 BCE), and Thucydides documents their construction in his History of the Peloponnesian War . Yet, Thucydides does not explicitly identify and discuss the original strategic motivations behind the Long Walls. Instead, what we learn about the function of the Long Walls comes at the outbreak of the Peloponnesian War when Thucydides has Pericles characterize Athens as unassailable, should the Athenians adopt a strategy that relied on their naval supremacy and conduct themselves as if they were islanders. The Long Walls were integral to Pericles’ concept of Athenian insularity, as the area that they enclosed became, in effect, an island. Therefore, the Walls are presented as insularizing technologies, since they made it so that Athens could only be attacked by sea. But what images or “historical” examples might Pericles’ appeal to insularity have evoked in the Athenian mind? To explain this, the themes of sea power and insular defensibility will be examined as they appear in an intellectual product of the Pentekontaetia, Herodotus’ Histories. The military architecture of Aegina and Aegina’s rivalry with Athens will also be considered. It will be argued that late archaic Aegina was a temporally and geographically immediate example (for Athens) of how a polis could acquire commercial wealth and maritime power by possessing a strong fleet and occupying an insular position.