So on a basic level, the Romans did not do that. At least not as far as you tell it as “copy and pasting.” While we look back at their pantheons and gods that match up pretty well — gods that the Romans and Greeks even associated (e.g. Ovid’s retelling of famous Greek myths in Latin using the expected parallels) — and we might assume that well obviously the Romans just stole it from the Greeks. There are even multiple memes to that effect circulating on various Classics and myth affiliates meme pages!

However, it is probably a good rule of thumb that if you can reduce it to a meme, it probably isn’t historically accurate, or at least it is more complicated than that.

So before we get the “it’s more complicated” aspect, let’s give this meme it’s due and grant where it does have a point. Roman culture did owe so much to Greek culture. Cicero borrowed a significant amount of Greek philosophical language, because Latin didn’t really have any.

Epic meter was borrowed wholesale, and I’m not a prosody expert or anything but I’d imagine taking this meter, which is formulated for one language with its own tics and adapted for a different language would be a little awkward. And speaking of poetry, Rome’s national epic is the first great instance of fan fiction! (This is admittedly reductive as Aeneas had been previously a bit associated with Rome’s founding in some traditions but the Aeneid is where it became “canon”).

And, finally, yes, as the adaptation of Aeneas’s story into the founding myth of Rome might indicate, the Greek gods and myth more broadly contributed a lot to the Roman pantheon.

Some of this is due to widespread Philhellenism in Rome. Greek culture was cool so they borrowed it (and when they conquered Greece, they stole everything that wasn’t literally impossible to move). And indeed some gods were adopted from other cultures that did not exist in Rome before: Isis, Magna Mater both come to mind. Bacchus perhaps.

Yet, regarding the core pantheon of Jupiter and Diana and others, this borrowing of myths and icons risks over-inflating the importance of these myths. They weren’t theology. They were cool stories from the prestige culture and there were lots of artifacts to steal, but it is important to distinguish this from the idea that they stole the Greek gods as in stole their religion. That did not happen. Roman religion remained itself, even as it could incorporate the Greek gods as syncretic versions of their gods in their pantheon (as well as some gods that previously weren’t part of their pantheon).

So if the Romans didn’t steal everything, why are their gods rather similar? Well because the Greeks and Romans are from the same language family, living in pretty similar climatic regions, are geographic neighbors. These two cultures did not develop independently. The evidence I always found most clarifying vis-à-vis the common ancestry of many aspects of the Greek and Roman pantheon is linguistics. (And linguistics is way outside my wheelhouse, but this particular etymological history is pretty straightforward).

So Latin and Greek (and English and German and Hindi and dozens of other languages) are in a language family known as Indo-European. All this means is they have a common ancestor in the form of probably some tribe of peoples who lived in Central Asia way way long ago (I’m on shaky grounds with any specifics to this point, but I hope the overall picture is clear). A good example of this is mater, mutter, “mam”, phonetic for मां (mom) in Hindi. So what can we do with this connection?

Well I’ll use Zeus and show how Jupiter existed separately from Zeus in the Roman pantheon despite being rather similar in terms of what role they served in their respective pantheons (I.e. king, sky god)

So Linguists have made some educated guesses going back and reconstructing some aspects of Proto-Indo-European, that old mother tongue. And they have showed that Jupiter (Jove) and Zeus have a common linguistic ancestor in the Proto-Indo-European word meaning sky and heaven, and god. And they they are also linked to देव (deva, god) in Sanskrit as well as Deus (Latin, god) (this particular link is given away quite nicely in the oblique case forms of Ζεύς : Διός).

Sources: Beard, North, and Price “Roman Religion” is a go to book for Roman religion which will give you a far better look with way more nuance and detail than I can provide here.

I’m not an expert in linguistics at all, but in casual perusing of it over the years of being immersed in Greek and Roman history, culture and language I’ve never heard or read anything contradicting the basic story I tell here (albeit no doubt in a very simplified form).