Since this was to be a full-scale invasion, it required long-term planning, stock-piling and conscription.[21] It was decided that Xerxes' Pontoon Bridges were to be set up to allow his army to cross the Hellespont to Europe, and that a canal should be dug across the isthmus of Mount Athos (rounding which headland, a Persian fleet had been destroyed in 492 BC).[22] These were both feats of exceptional ambition, which would have been beyond any contemporary state.[22] However, the campaign was delayed one year because of another revolt in Egypt and Babylonia.[23]