“stake.” The Hebrew is literally “tree” or “wood.” It was a wooden stake. The stake itself could not have been 75 feet, for one thing, there would be no way to get Mordecai’s body up to the top of it. It was on some wall or platform as a base, then placed on top of that such that the top was 75 feet off the ground and easy to see. The Assyrians and Persians did not hang people from the “gallows” by the neck like Westerners are used to. Instead their custom, documented as far back as the Code of Hammurabi about the time of Abraham, was to impale people on a stake. Usually the stake went through the front of the body and under the rib cage, and this practice can be seen in the Assyrian base-relief rock cut that was made celebrating the Assyrian victory over the biblical city of Lachish. The victim was “hung” on the stake, but not hung by a rope. He was hung, or suspended, on the stake. Many versions say “impaled” instead of “hung” for clarity (cp. NAB; NIV2011; NLT; JPS Tanakh; translation by Robert Alter).
Haman was “the enemy of the Jews” (Esther 3:10; 8:1; 9:10, 24), and a representative and prophetic picture of the Devil himself. Haman schemed to kill Mordecai, the figurative head of the Jews by hanging him on a stake, and thus rid the earth of God’s people. The Devil schemed to kill the Messiah on the cross and by doing so get rid of the Messiah and God’s people, who then could not be redeemed. But God worked to turn the schemes upside down. Haman was impaled on his own stake, and instead of killing the Messiah and God’s people, Jesus’ death on the cross insured the death of the Devil and the salvation of God’s people.
“75 feet high.” The Hebrew is “50 cubits,” which is about 75 feet or 23 meters.