Perhaps that's what the artist/architect does, apply form to content. Yet, in the case of Piranesi's Ichnographia Campus Martius at least, it is the form within a context that discloses the content (if the observer is astute enough to find it)--the content is implied rather applied.
Of course, but more specifially signifying the union of Mars and Rhea Silvia, which issued forth twins: sacred and profane. What else would expect from the coupling of a god (of war) and a (vestal) virgin?
No doubt some architecture speaks for itself.:
Steven Izenour was born yesterday 67 years ago.
I like it when content takes on a form that is very easily recognized yet not very easily digested.
Yet some people might still argue that anything looks better with a frame.
Did someone mention cocktails?