I tell my students to start with a Google of the author. Is s/he affiliated with a university? With a think tank? NGO? Each of these will have differing goals in publishing, and you need to weigh them when considering a source.

Then read her/his CV, paying attention to what has been published and in which journals. Is the author publishing stuff in the Journal of American History? If so, probably reliable. Is the author publishing stuff in the Journal of Crazy Conspiracy Theories? If so, maybe not as reliable.

Is the book published by an academic press (University of Somewhere You've Heard Of Press, etc.?) If so, it has most likely gone thru a pretty rigorous peer-review process. That doesn't guarantee a good book, but it does mean that at least a few people think it's probably OK.

Thumb thru the citations. By itself, footnoting doesn't mean anything. Heck, I can cite Phil Foner all day, but that doesn't mean it's a good thing. Are the footnotes citing someone reputable? Are the notes to works that are as describes above (academic presses, solid journals, etc.?) Do the notes include historiographic discussion? (nb: historians, if allowed by a publisher, would probably write a 5000 word article with a 25000 word set of footnotes politely bashing or congratulating their colleagues.)

This list is far from exhaustive, but should give you a fair footing.

Cheers and keep reading.

A good start is to look at the sources used. A respectable work will have pages and pages of works cited at the end. That's not a guarantee, but it is a helpful place to start looking.

Sadly there's no hard-and-fast rule, or database for reliable sources. Every source carries with it some degree of bias or inaccuracy, and it's part of the historians job to work out the degree to which this exists.

Your question seems to be referring to works of history as opposed to primary sources (i.e. first-hand data, records, images etc.). The only way to tell if the information they are providing is accurate is by checking these original sources. It's likely that if you are reading from widely-available or academically published texts that the sources they are using are reliable (or at least accepted as useful by the historical community) and if they are good historians they will discuss the problems that arose from the sources they've used. For a period such as Rome it is very hard to find source material that doesn't have significant problems in it's provenance, so most reputable historians should be taking these into account with their analysis.

I think what you're getting at is whether their analysis and the conclusions they are drawing are up-to-date, and again this is a bit of a nuanced question. For instance, Bryan Ward-Perkins' argues in The Fall of Rome and the End of Civilization that the traditional view of the fall of Rome, (that it did mark a serious material and societal decline) argued by Gibbon et al still holds true, but not for the reasons Gibbon put forward. Therefore Ward-Perkins is arguing that while he is rightfully 'debunked', his points still stand. Post-modern and Marxist historians would most likely disagree. What is accepted by some as a good interpretation of events will inevitably be rejected by others. For this it's useful to read (or listen) to works discussing the historiography of a period, which will hopefully give you an impression of what is still worth reading, but at the end of the day you have to choose who to believe. No-one has a monopoly on historical knowledge, although you will find that the more obscure the subject area the smaller the pool of 'strong' works of history exist. As for Rome there are many reputable historians and works of history which are worth reading, and I really recommend Ward-Perkins if you're interested in that period.

We did a Monday Methods thread on critical reading that you might find helpful!

It's difficult for the layman to determine good vs. bad sources sometimes. A few indicators, though not guarantees, of good sources will be:

1. They are published with a reputable press. Be wary of anything published with a press that sounds like it's run out of the author's garage, because it probably is. University presses aren't going to publish terrible books on the whole.

2. They are not an "independent scholar." Some times, though not always, this means that this person is under qualified or has wacky theories that have kept them out of the academy.

3. If you have access to academic journals, read a few book reviews on the book. If other scholars in the field are engaging with it, that's a good sign. If they all hate it, that's probably not a good sign.

It gets easier the more good history you read.

If you were to go to graduate school, you'd spend the first two (or more) years reading a lot of books and articles and discussing how their arguments were put together, how they used their evidence, whether their methods were credible and convincing, what they did wrong (etc). At first, it's hellishly difficult because - as you know - it's very hard to evaluate the quality of an argument when you're still learning the basic story (which the author often assumes you already know). If you have to stop and look up every single source to see if it's being cited properly, it's veeery slow going. But after you've read a few good books on the same subject by different authors, you start to see how they fit together because - especially when you study something like the Roman empire - they're talking about the same primary sources, referencing the same important books by other (modern) historians, and actually having a conversation with each other. Once you've read enough to understand how that conversation fits together, you'll quickly see when a book does something different; bad of fringe history is usually very easy to recognize once you're steeped in enough good history.

So to start, I'd recommend reading through a list of known, trustworthy books about the Roman empire - we have a book list here with some great recommendations, and we'd be very happy to point you toward other good books on specific topics that might interest you if you ask us.

As you read these vetted books, look at how they back up their arguments with evidence. What sources do they use to support their arguments? If one source keeps coming up again and again, consider looking it up and reading it (many of the sources Roman historians use have been translated into English, and are available free online). What are the ways they use these sources, and what are the ways they don't (lots of pop historians read original documents from Rome as though they were ripped from a modern newspaper, but real historians are much more careful to read sources in their own context - and good historians will often explain why they choose to read a particular source in one way and not another)? After a while, you'll start to get a feel for how real academic historians write and use our evidence, and it will begin to be very obvious when something fails to pass muster.

We also have a few professional shortcuts for tracking down good books. We rely very heavily on reviews by other academics, and - for ancient history - you can find a lot of these for free online. The Bryn Mawr Classical Review is a fantastic place to see in-depth reviews by qualified experts of most of the latest books on the Roman empire, and you can subscribe to their email list to stay on top of the best recent publications. As a general rule, if a book you want to read hasn't been reviewed by BMCR, and wasn't published by a university press (or another press that you see all the good historians you've read citing all the time), it might be suspect.

Another thing that hasn't been said by now: Critical reading. Is the author making claims he possibly can't know? (Like Napoleon at a secret meeting said:"..."). Does it feel like the author makes statements with dubious claims? Both of those often happen in biographies.

Does it read like a novel? This isn't inherently wrong, but often it is indicative of less than rigorous argumentation.

I would add that once you have read a few established historians you should be perfectly capable of coming to your own opinions on how trustworthy a source is. Any historian can find bones to pick with any other historian. That's how we keep the field alive.

So here's a quick list to help any budding Roman historian get a good grounding:

Roman society:

Super readable: Mary Beard's book on Pompeii

Scholarly: Claud Nicolet's World of the Citizen in Ancient Rome (I would use it as a reference. Might be hard to find outside a university)

Primary Sources: Pompeii, Catullus, Cicero, etc.

Roman Republic

Super readable: What the heck, go for Robert Harris's Imperium. It's historical fiction about Cicero but does a good job. I've never met a historian who hated it. Also HBO's Rome. Skip the second season if you aren't totally enthralled.

Scholarly: Erich Gruens Last Generation of the Roman Republic. Once you make it through that, you're practically ready for your comprehensive exams.

Primary Sources: Polybius (esp. Book 6), Livy, Appian, Caesar

Roman Empire

Super Readable: I, Claudius, though it is a little too conspiracy driven. There are a ton of biographies for the emperors. Yale did a series, so look for Yale University Press.

Scholarly: Yale UP books are scholarly but also mostly narrative.

Primary: Tacitus, Suetonius, The Augustan Histories/Lives of the Later Caesars, Ammianus Marcellinus

Jumping in with a related question, what's the best way to tell how reliable a primary source is? I hear all the time about how this or that historian of antiquity was exaggerating or had an axe to grind, and obviously historians have done a great job correlating or debunking a lot of it, but how does a layperson tell?

Some academic search engines will show how many articles cite an article you pull up there. Obviously if it's new work you need to discount it a bit, but if you pull up a decade old paper that's been cited 5 times and isn't on a super narrow topic, that should set off warning bells.