My guess is that Port of Spain and the like are full names, hence no articles; if you said the Port of of Spain it'd be understood as the port of Spain - as if you were talking abt a definite Spanish port, one of many others.
I don't think The Islamic City of Marawi is marked so on the maps, it's just a set expression that provides some additional info; in the same vein one could say the multicultural city of N.York. As to the capitalization in the former I guess it just reflects the religious reverence.
Sorry, I disagree. If they were complete names, I'd know them in Russian - just like Port of Spain. I wonder how San Marino can have its complete name with an English word - is English the official language there? I wish somebody more learned in geography gave the answer.
Proper (place) nouns, their spelling, pronunciation, articles and prepositions are the exclusive property of the people who live there. There is not one single answer for all of the variation we hear. Every native can tell you his own favorite place-name story, no matter where he lives.
I wonder how San Marino can have its complete name with an English word - is English the official language there? I wish somebody more learned in geography gave the answer.
We're talking about the official English translations of the names. The language spoken in San Marino is Italian.
That said, the official name in Italian appears to be without the definite article: "Cittā di San Marino" (not "La Cittā..."), so it would literally be translated as "City of San Marino". However, that sounds inelegant in English, and we prefer either to use the definite article -- "the City of San Marino" -- or to use a different construction -- "San Marino City".
"The City of...", in parallel with "the city of..." (where "city" is purely a description, not part of the actual name) is a set phrase. You simply have to use the definite article here.
There are many place names which, in English, require the definite article. These include: the Hague and the Central African Republic, for example. Conversely, there are many places which require the definite article in its native language, but not in English: Iraq is one.
Of course, you won't see any place names with the definite article in Russian. Russian doesn't have a definite article.