I've never seen any rules regarding the usage of the definite article with the names of cemeteries, memorials and gates.
Could some native speaker please read my assumptions below and decide whether they're correct?
Before I start, I would like to quickly review the "categories" that are frequently used when describing the usage of articles with proper nouns:
I. Never use "the" with the name of <structure, building...>
II. Always use "the" with the name of <structure, building...>
III. PROPER NOUN + <structure, building...> = no article, COMMON NOUN + <structure, building...> = THE (
The White House X
0 Buckingham Palace)
IV. No obvious rules at all

1) From what I've read and heard, I've come to the conclusion that the definite article is always used with the names of memorials. I.e. the names of memorials fall into category II. Some examples:
The Menin Gate Memorial
The Vimy Ridge Memorial
The Saint Julien Memorial
The Vietnam Veterans Memorial
The Normandy American Cemetery and MemorialIn Europe, there are many war memorials called e.g. "
The Canadian Memorial",
"The Australian Memorial" etc.
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2) I'm not sure about cemeteries. I've seen the names of many famous cemeteries without the article, e.g.:
Arlington National Cemetery
Tyne Cot Cemetery
Pere-Lachaise Cemetery
Calverton National CemeteryOn the other hand, I've seen some names of cemeteries in non-English speaking countries that contained the definite article even though the names of the cemeteries followed the "PROPER NOUN + Cemetery" pattern.
And what about "
The Normandy American Cemetery and Memorial"? What if I remove the "
and Memorial" part? Will I have to remove the article as well? I'd say so.
What if someone decides to start their own cemetery and calls it, say, "
White Cemetery"? Will it have the article?
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3) I used to think the names of gates (and triumphal arches) always take the definite article. Examples:
The Menin Gate
The Ishtar GateHowever, today I've come across
India Gate (without the article). I see absolutely no system here because
Menin,
Ishtar and
India are all proper nouns.
That's all. More on articles in another post

.
As always, thank you very much for your patience.