For Americans, the title of the play might provoke a bit confusion, but for British people, the hymn "Jerusalem" (based on a poem by William Blake) is an iconic part of national heritage. The play name-checks Blake and even includes a passage of the hymn, which runs in part:
And did those feet in ancient time
Walk upon England's mountains green:
And was the holy Lamb of God,
On England's pleasant pastures seen!
And did the Countenance Divine,
Shine forth upon our clouded hills?
And was Jerusalem builded here,
Among these dark Satanic mills?
In the play Jerusalem, though, just after the word "Satanic" thumping music starts to play and the stage is transformed into the trailer home of the protagonist, Johnny "Rooster" Byron, played so memorably by Rylance. His name is an obvious reference to another Romantic poet, George Gordon Byron, whose specter haunts the play.
Lord Byron was as famous for his sexual exploits as he was for his poetry (perhaps even more so). When the play's "Rooster" Byron is threatened with expulsion from his illegal dwelling after a crisis meeting in the village hall, he remarks that he "shagged" one of the leading complainers only last June. Butterworth's Byron is not a poet by trade, but a daredevil who once leapt over rows of busses on his motorcycle, though he has now declined to selling drugs to local teenagers.
But there is a certain poetry in the lies he tells, including his tall tale of meeting a giant who built Stonehenge. The giant supposedly gave him a drum, telling him that if he ever needed help, he should beat on the drum, and giants will hear it and come to his aid. His companions mock his story at first, but when he challenges one of them to beat on a drum inscribed with something that looks like runes, the companion declines, just in case the giants might actually show up and be miffed by a false alarm.
Though Lord Byron was a lover and a poet (in addition to being a fine dramatist, penning plays like Manfred), he died a man of action, fighting for Greek independence against the armies of the Ottoman Empire. When the police come to evict him at the end of the play, "Rooster" Byron's friend warns him, "They got an army." Though we don't see Rooster die onstage, as Lord Byron died in Greece, Rooster's mad drumming at the end of the play could be seen as a symbolic death.
Butterworth's writing is quite powerful, and Jerusalem is a play well worth seeing, with or without Mark Rylance.