During my research to prepare my answer to this question over on /r/historywhatif (yes, I know) I found out that contrary to my believe we actually do know quite a bit about Aelius Gallus's campaign against Arabia Felix during the reign of Emperor Augustus. I was especially delighted to read /u/Celebreth's tremendous account on why his campaign failed.
Now Wikipedia mentions that Aelius Gallus also managed to conquer Medina and Mecca, at least for a short period of time. Since said page also features the infamous "Citation Needed" flag I was just wondering if this is true – and if it is (which I assume for the time being), what did the city of Mecca look like when the Romans arrived there? I understand that this might not be easy to answer since we know that during the early days of Islam most if not all pre-islamic sites within the city were razed and for obvious reasons nobody could ever conduct any archaeological surveys – so how much do we really know about the city?
There is no reliable mention of a place called Mecca before the 8th century CE. There are zero ancient references worth considering (in my opinion), and the evidence suggests that Mecca either did not exist at that time or was so small and unimportant as to not be mentioned in lists of notable places. Diodorus Siculus vaguely references a "shrine" of some sort, but the geography does not work at all, since he is talking about the northwest. Ptolemy lists the names of 50 notable sites in Arabia, one of which is "Macoraba," but most modern scholars are very skeptical that this has anything to do with Mecca, and again the geography does not work. The late Roman historian Ammianus Marcellinus also makes a list of notable sites there, but does not make mention specifically of any word which even remotely relates to "Mecca" linguistically. If it existed at all in the time of Gallus, it was extremely small and probably would be mostly invisible, archaeologically speaking.
I agree with /u/Alkibiades415 that wikipedia plainly has this one wrong. For an extensive discussion of why all of the supposed ancient references to Mecca are almost certainly wrong I would point you to Patricia Crone's Meccan Trade and the Rise of Islam.
That book also goes into detail about why it's very hard to answer the question of what we know about the city, if indeed it even was a "city" per se.
To reiterate, in Crone's words: "[of Mecca] there is no mention at all, be it in Greek, Latin, Aramaic, Coptic, or other literature composed outside Arabia before the conquests." Much effort has been made by scholars (and by Muslim believers who want validation) to connect Mecca to various places mentioned by those ancient sources, but none of them hold up. I suspect this wikipedia article is a similar such effort.
Edit: looking at the /r/historywhatif post, it looks like the premise of that question falls into the same trap that Crone is also trying to dispel throughout her book. Namely that the "trade routes" that the Romans needed for eastern luxury goods were coming overland in Western Arabia and that it might have been possible for them to have "secured" them. The fact is, all of those goods were coming in perfectly well by sea and there is no evidence that there was any such overland trade in the Hejaz of luxury goods bound for Roman territory, in contrast with the extensive evidence of the Red Sea trade.
Again, I would say that if you have a deep interest in this that Crone's book is worth finding. It's short and highly readable.