There is another interesting thing about the Seven Gates: The fact the Seven GATES is a pass is not mere coincidence. In History, two other passes with the word Gate in their names were attacked or invaded.
1) The Thermopylae: In the year of 480 BC., Xerxes, the Great Persian King, was trying to invade Greece through the center (Thessaly). Leonidas I, the king of Sparta, led 300 Spartan soldiers to the Thermopylae (Hot Gates in Greek), and would have defeated Xerxes' army if weren't for the betrayal of Ephialtes.
2) The Persian Gates: After Alexander the Great defeated Darius III, the last Persian king, at the Battle of Gaugamela, in 331 BC, he began his conquer of the Eastern half of the Empire. When he reached Persepolis, Ariobarzan led a bunch of Persins patriots through the Persian Gates, a pass near the the capital of the Persian Empire.