Clashes were also taking place Friday at a military barracks close to Maarat al-Nuaman, a town on the main highway to the northwestern city of Aleppo which was seized by rebel forces earlier this week, the Syrian Observatory for Human Rights said.
Source:Syria activists: Jihadists seize missile base - Israel News, Ynetnews
barracks noun - definition in British English Dictionary & Thesaurus - Cambridge Dictionary Online
Does the indefinite article "a" make the picture clear that just one barracks being captured since "barracks" can be functioned as singular & plural at the same time? Also, I don't know whether there is a specific label for these kinds of nouns.
These "barracks" could be one or more buildings on the same site.
Yes, the "a" tells you that it is just one site.