DC has few statues/sculpture compared to a European capital city, but what is does have is pretty high-quality IMO; a notable collection from an artistic standpoint really that is worth visiting and should be more famous.
Obviously Lincoln memorial
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Korean war memorial
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Grant, staring implacably down the mall at Lincoln
next to Grant, battle scene:
Methodist preacher in Columbia Heights
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Iwo Jima memorial
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And of course, Washington DC's weirdly buff statues on the bridge into Arlington cemetery:
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