Roman senate trad. portrayed as round, but actual bldg in Forum is rectangular. Why?

In just about every filmed or painted representation of the Roman Senate, the Senators sit in a round building, seated on round marble "bleachers surrounding the room’s center. There’s also a famous model of the ancient city repeatedly pictured in books about the city, which also shows a round Senate building.

But the actual building they show you in the Forum is rectangular. Why is this? WAs the rectangular building a later replacement, or was it used earlier? Incidentally it’s one of the best preserved structures in the Forum, largely because for many centuries it was used as a church.

I think that the square portion you’re used to seeing is only the entry way with columns, this gave way to a round dome in which one would suppose the senate did it’s yelling and screaming.

Wait until a professional Roman scholar comes along as tells me I’m full of it…

I don’t think that can be it; the remaining building is large and fully gives the impression of being the main structure, and IIR there’s a steep, almost cliff-like incline behind it, so there’d be no room for any missing round part.

According to this page, the present Senate building dates from the time of Diocletian, in the 200s AD. So , unless thee are other indfications (like old foundations or something), the Senate building during the last days of the Republic could’ve had any shape:

More on the Curia (Senate Building):

I’ve always preferred the Senate building in Kubrick’s Spartacus, myself – it seemed clean and elegant. But the one in the current HBO Rome seems pretty nice as well. The one in the circa 1970 Julius Caesar looked drafty and crumbling.
I suspect most Senate chambers in plays and movies are made semicircular both to reflect outr own architecture and to provide some visual shorthand – “This is a semicircular gathering of seats, therefore it must be a governing chamber (since it isn’t a theater or arena)” – so they don’t have to come out and explain that it’s the Senate building.

My hunch would be that the movie sets were mainly inspired, directly or indirectly, by Cesare Maccari’s much-reproduced Cicero Denouncing Catiline in the Sala Maccari of the Palazzo Madama, the seat of the modern Italian Senate. Not for the first time would Hollywood designers in search of art-historical kudos have been looking to nineteenth-century history paintings.

And Maccari had probably been primarily influenced by nineteenth-century semi-circular parliamentary chambers, for which those in France and the USA were the obvious prototypes, but which, significantly, also included that of the Italian Senate.

And the original inspiration for those parliamentary chambers had not been the Roman Curia but Greek and Roman theatres.

There’s also the fact that the Senate did not always convene in the Curia. For example, when Caesar bit the big one, the Senate was meeting in an annex of Pompey’s Theater near the Campus Martius. The location for senatorial meetings, like many other aspects of Roman life, was determined by reference to a host of obscure and arcane rules.