I think it's totally likely, especially as you have a relavent specialization. While typically author's have a university/academic connection this is not always the case- and no doubt depends somewhat on the journal and field.

I would say there is no reason not to expect that you could get a piece published. You would likely want to make connections with people in the field if possible who could review your research and writing before submitting it to a journal- it helps to get a vote of confidence and make sure there are no glaring absences, omissions, or errors in your piece before it goes to an editor and then blind reviewers.

In terms of making connections, I would check and see if there are any relavent conferences or historical associations where you could present any work that you do. This can be a key place to get feedback and find other scholars interested in similar questions. This is more likely something you might want to do after having begun some research; but it might also be useful to attend some talks on the subject before diving too deep just to get a feel for how people talk about it.

I'm far from a historian of Rome, but I would imagine there is some language learning or competencies you may need to work on well. At least in my respective fields it can be a bit odd if an author is strictly anglophone- though not unheard of.

The people who referee your work will not know who you are or what your qualifications are; peer review is double-blind. They will look at your work and your arguments, provided they meet the basic standards of the editorial office (length, simple depth of work, appeal to audience, etc.). If they hold up and display familiarity with the field and its conventions, it is just as likely to meet the standards of publication as any work by another scholar. You don't have to submit your credentials when sending in a manuscript, after all. Working in journals, we had a few "independent scholars" publish essays; some had doctorates in history, but some had qualifications in something else and came to history-writing secondarily. Yes, we had one lawyer, and he wrote on legal history--though he had a small bit more training in history proper, it wasn't much.

Basically, yes, if you do the primary-source research, situate it well in context (historical and historiographical), and make a case for relevance, there should be no reason you can't get an article published. As a lawyer, you certainly know how to present information and cite your sources (though I would suggest putting it in whatever format your target journal uses which will dispose editorial staff positively towards you), so that is not a worry. It all comes down to whether you can engage with the field and make your thesis convincing and support it well.

So actually my answer would be "very possible," based on my experience editing. It may be different if you happen to hit a snobbish journal or something like that, but I don't know [how common those are in your prospective field]. I would strongly encourage you to go for it, because some of the best new observations--or at least the ones that get people talking in new ways--come from those outside of our bubble.

[edit: clarifications; also seconding /u/b1uepenguin 's suggestion that you may want to have a friendly reader before you send work out--a good number of academics are willing to do that for promising researchers in their field.]

As the other two responders have noted, I think you sell yourself a bit short when calling yourself an "autodidact." You have a terminal degree, albeit one in law rather than history, which means you do have experience with high level thinking and research. Many professors of legal history have JDs rather than (or often in addition to) PhDs. In fact, a professor I had in undergrad who had both a JD and a PhD recommended that if any of us wanted to become legal historians we should consider a JD, given the broader applicability of a JD and the much shorter time to completion.

Thanks for the help, everyone. I think I'll go for it, then.