Vietnam plays against the grain of most Civilization VI strategy — its civ ability, "Nine Dragon River Delta," actually restricts where land specialty districts can go, in exchange for turning that restriction into a defensive fortress.
Land specialty districts can only be placed on Rainforest, Marsh, or Woods tiles — a real constraint, not just a preference — but buildings inside those districts produce bonus Science, Production, or Culture depending on the terrain feature underneath, and the terrain itself stays in place (still giving its normal adjacency and defensive bonuses). Vietnam can also plant Woods as soon as Medieval Faires is researched, well ahead of the Conservation civic other civilizations need.
A Medieval era unit (corrected from an earlier "War Elephant-tier" description) that replaces the Crossbowman. It starts with 5 Movement when beginning its turn on Woods, and can move back onto Woods after attacking to repeat the cycle — devastating for grinding down a besieged city.
A district unique to Vietnam that replaces the Encampment. Unlike land specialty districts, the Thành is not restricted to Rainforest/Marsh/Woods tiles, since it does not count as a specialty district and has no population requirement.
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