A Horse with No Rider

This horse with no rider
Shall carry us all, Agamemnon
Yes!

This is a prize that they'll never resist
There are some volunteers we should enlist
Some of you Spartans would make a good choice
How'd you like to spend some time in a horse?
Just a little cunning to perfect this plan
Not too obviously underhand
And to make sure they move it inside their walls
We need to find a stooge, a fool

Simon, you're perfect
Hurry up and get drunk
We'll leave you behind
They'll have mercy on a man who appears to be
Out of his mind

Thank you, thank you
Of you I could murder a drink
Now move!
What is going on here?