Roman representative democracy

[Chapman]

Travel expenses can be paid for by taxes

They can be for sure but that wasn't laid out in the OP. Further than that concern alone though; are these elected representatives paid for their time? Do they draw a salary from provincial coffers? If not, once again I think we return to the same problem - money. Especially in this time period the average citizen probably doesn't have the luxury of "taking time off" to travel to Rome for an unclear amount of time to serve as representative. And I can't honestly see the wealthiest class in Rome feeling so generous towards those "beneath" them. Not only are they now paying taxes to send these reps to Rome, but they're giving them a salary too? Paying the travel expenses and the salary of people who don't represent their interests and probably want to take a bigger chunk of their wealth? At that rate they definitely might as well run for the seat themselves, then give away whatever salary they receive as a way to "thank" their voters. Or, support the campaign of whoever sucks up to them best and their ultimate reward is the office and its salary. Either way, it seems like you run into many of the same problems.

 

[Galba Otho Vitelius]

Technically it was doable. The tech in the high middle ages, when representative assemblies were invented, was no different.

There was a legal issue in that until the 3rd century AD, the Roman empire under both the Republic and Empire was mostly nominally independent cities and kingdoms under Roman protection or administration. Legally, "Rome" was a checkerboard pattern of cities and colonies. The provinces at least started as military commands.

This started to change in the 3rd century, first with citizenship being made universal to not-slaves throughout the empire, and then towards the end the empire being reorganized as a unitary, bureaucratic state (reforms associated with Caracalla and Diocletian).

However, until then the best you can do is to provide for legions stationed in the provinces to send representatives to some sort of military assembly, and for some allied cities to do so to. The only people in the elite that would be interested in doing something like that would be the generals. And they would be leery about doing this for the legions and cities allied with rival generals.

An Emperor could do something like this, and even something like a council of the provinces. But the Emperor would still be in charge of the empire. He would only do this if it would be in his interest, basically to raise more taxes.

However, its telling that no one was even thinking in these terms until the 13th century. It seems you need the decentralization of feudalism to get people to even think in these terms (and it was only attempted in feudal western Europe). The trend during the imperial period was increased centralization.