The "Hexamilion" stands at the end of a long series of attempts to fortify the isthmus stretching back to perhaps the Mycenean period. Many of the Peloponnesian cities wanted to pull back and fortify the isthmus instead of making a stand at Thermopylae when Xerxes invaded in 480 BC (Herodotus' Histories 7.206). The issue arose again before the Battle of Salamis (Herodotos 8.40, 49, 56). Although the concept of a "Fortress Peloponnese" had been repeatedly suggested, fortification of the isthmus was of no utility without control of the sea, as Herodotus notes (7.138).