It was said that the army of Xerxes took seven days and nights to cross over the Hellespont. The number seven was of course intimately associated with Ahura Mazda, however it is also a number of Benjamin/Joshua. This is also reflected in the earlier campaign of Datis. The city of Eretria was betrayed on the seventh day from within (figuratively, "the walls fell outward/flat"). The city was not spared by Datis/Xerxes.
In addition to striking the waters of the Hellespont, Xerxes also branded them with hot irons. It's not clear what the typological significance of this was. The only thing that comes to mind is the floating axe head of Elisha (2 Kings 6).
The bridge across the Hellespont was constructed of two sections, one containing 360 ships and the other 314 ships. There is likely some number symbolism associated with those choices.
Prior to the invasion, Xerxes had the "eldest son" of a man named Pythius cut in two and caused the army to pass between the halves of his body. This strange sacrifice is reminiscent of the covenant between Abram and "the Sovereign Lord" of Genesis 15. In this passage, the Lord promises Abram an heir. Abram eventually has two sons, one by Hagar (who was probably a daughter of Mamre/Gideon) and the other by Sarah (sired for him by Abimelech/David).
Abram was instructed to cut in half a three-year old heifer, goat, and ram. The Lord then caused a fire to pass between the severed pieces.
By associating himself with this bizarre covenant, Xerxes is asserting himself as the "Sovereign Lord" of the Persian dynasty with its fire god Ahura Mazda (Thoth/Shamash). As such, he is also claiming the right to produce the next generation of royal heirs, and particularly as a new Gideon/Mamre/Judah and a new David/Joshua/Benjamin.
Regarding the canal that Xerxes ordered to be built, it was Herodotus that stated the canal was not necessary to support the campaign.
© Charles N. Pope, US Library of Congress. All rights reserved.