That's only the final part of that poem, Stilly, and misses the three-line paragraph breaks ("like the 'tercets' of the British Druids"). It begins:

I love liberty; I detest tyranny.
I have always been a patriotic Roman.
The Roman genius is Republican.

I am now, paradoxically, an Emperor.
As such, I exercise monarchical power.
The Republic has been suspended for three generations.

The Republic was torn by Civil War.
Augustus instituted the monarchical power.
It was an emergency measure only.

.... that may help searching. You got the core of it, but read both books for the context and the full flavour.

Hope that helps.