WI: Roman Constitutional Monarchy?

The possibility was brought up in this thread and it seemed plausible to me. So lets say that Caligula avoids the illness that drove him mad, or at least managed to keep it more-or-less in check, and he continued to 'democratize' the Empire to such a degree that, after his death, Rome is left in a situation that power is balanced between the Emperor and Senate/bureaucracy that is at least partially representative of the middle class. Lets then say that this gets codified into a constitution by someone - I'm not sure who would have had the ability and inclination to do this - and Rome is officially a constitutional monarchy with some real democratic elements.

How does this progress?
 
Until Vespasian it was nominally that, with the senate having de jure extensive powers. The fact that the Senate always agreed with the Emperor or abstained reflected the reality. It's just like how British Monarchs can dissolve parliament at will and they have an extensive list of reserve powers that probably aren't going to be used until a situation the monarchy itself is in danger like a nuclear war (I can't even imagine a situation where parliament cancels the European Declaration of Human rights by either uber-nationalism or a CONVENTIONAL war with China with parliament mishandling the war by passing a bunch of stupid Acts that make Generals do dumb things would warrant Elizabeth II to use her reserve powers) so ironically both the early Roman Empire and Modern United Kingdom are constitutional monarchies, with the former monarch having more de jure powers and less de facto powers.
 
I don't know how you would get the Senate to become representative of the middle class. Before the Empire, censors, for the most part, appointed senators from upper class; and afterwards, they either had to be a son of a senator or appointed directly by the Emperor. Regardless of how this system is formed, it's only a matter of time until an ambitious general seizes the moment and overthrows the old order, using the Senate as a sort of approval committee instead of giving it actual power.
 
Top