The keyword phrase "September 11th towers" functions grammatically as a noun phrase. The core component and main point of this phrase is the plural noun "towers".
In this construction, "September 11th" acts as an adjectival modifier, specifically a noun adjunct. A noun adjunct is a noun used to describe another noun. Here, the proper noun "September 11th" (representing the date of the attacks) modifies "towers" to specify which particular towers are the subjectthe World Trade Center towers involved in the events of that day. The head of the phrase, which dictates its grammatical role in a sentence, is "towers."
Therefore, for the purpose of an article, the primary part of speech is noun. The entire phrase refers to a specific set of entities (the towers) and will function within a sentence as a subject, object, or complement, just as a single noun would. The focus is on the physical structures, qualified by the historical event.
