The bombard hero unit Jean de Lorraine in "The Siege of Paris" is based on a minor character in Mark Twain's Personal Recollection of Joan of Arc, cannonmaster Jean le Lorraine.
The Definitive Edition set of challenges is called "The Art Of War". Its scenarios even quote lines from the namesake book.
In the fourth campaign mission of the Jan Zizka Campaign, "The Golden City", in Dawn of the Dukes, around the 40-45 minute mark, Emperor Sigismund will send a Trebuchet at you with the line "Now I have a Trebuchet. Ho ho ho."
The second campaign mission of the Tamar campaign is called "Yury's Revenge".
Achievements
Losing 25 units in battle and still winning a match in the HD Edition nets you "Just a Flesh Wound".
Purchasing 20 Dragon Ships in the "Lake Poyang" Historical Battle nets you "Smoke on the Water".
Completing the "Lepanto" Historical Battle without letting a single Turkish transport ship land on your territory nets you "Battleship".
Converting Alfonso de Albuquerque without killing a Portuguese unit in the Francisco de Almeida mission "A Son's Blood" "Friends, Countrymen, Lend Me Your Ears".
Destroying an enemy Wonder with less than 100 years to go nets you "Final Countdown".
Killing 25 units with a Trebuchet nets you "It's a Treb!".
Creating 100 Throwing Axemen as the Franks nets you "Frankly My Dear...".
The Spanish have two related to Monty Python's Flying Circus: "Unexpected"note Convert 100 units using Spanish Missionaries and "Supremely Unexpected"note Win a match as the Spanish while only creating Villagers.
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