We find the reference to "Pandaemonium" here:

Mean while the winged Haralds by command
Of Sovran power, with awful Ceremony
And Trumpets sound throughout the Host proclaim
A solemn Councel forthwith to be held
At PANDAEMONIUM, the high Capital
Of Satan and his Peers (...)

"Wherefore with thee / Came not all hell broke loose?" (Book IV, lines 917-18)

A brief analysis of the phrase is found here ("pandemonium" gets a nod here too). Literature.org gives the context here.

wr ()()