The Last Debate and the Council of the Númenóreans

[Earniel]

A country the size of even Third-Aera-Gondor probably justified a senate. But since Gondor was a kingdom, and Rome took a lot of step to make sure they weren't one, that's probably one of the reasons why Gondor didn't have a senate.

Still, hard to imagine even able Denethor micromanaging the entire land on his own. Granted, the existance of the Palantiri probably helped a lot. Rome had to do without.