Where did As I look ahead, I am filled with foreboding; like the Roman, I seem to see the River Tiber foaming with much blood""). come from?
Rivers of Blood speech:  The expression "rivers of blood", which did not appear in the original speech, is an allusion to a line from Virgil's "Aeneid" quoted by Powell (""As I look ahead, I am filled with foreboding; like the Roman, I seem to see the River Tiber foaming with much blood"").
i don't know