The two quotations that are examples of imagery are:
“Have you not made an universal shout, / That Tiber trembled underneath her banks”
“And do you now strew flowers in his way, / That comes in triumph over Pompey’s blood?”
Imagery is the utilization of non-literal language to depict objects, acts, and thoughts in a manner that makes us use our physical senses. It is often considered that imagery employs certain words that produce visual depiction of ideas in our minds. In the examples above, we get that visual depiction in the description of river Tiber "trembling", and Pompey's "blood", which represents all the defeated soldiers laying dead or injured on Pompey's ground.