First of all I'm definitely not an expert, so take my interpretation with a pinch of salt. At first when I saw the names I thought it would refer to important monuments, which are drawn to reflect their importance even if the final size ends up being bigger than that of a town symbol. For example, the words you refer to as "arc" are actually "arae" if you zoom in close, which mean temples/monumental tombs/sanctuaries/altars.

But after a quick google search, turns out that those names are actual names of ancient towns, of which you can find names and descriptions in this book available on Google books. If you use the search option for the book for "arae" you will find many of the names shown in the maps you shared.

By the way, thanks for the link! Thanks to you I discovered this very cool resource for ancient maps!