The power of Boadicea is highlighted in this excerpt, using adjectives such as fierce, beautiful, and the imagery of "her golden hair blowing round her in the wind" giving the illusion of someone otherworldly, superior to common beings. Her speech rouses deep passion in the people, it's a call for action that is responded eagerly. Loyalty to the Queen is loyalty to the Country, the soldiers pledge their lives to her, hence they pledge their lives to fight for the country against the Romans. Her rage is mirrored and multiplied, till everybody is willing to die for her, to avenge their country.
This is an example of a simile, a comparison between two things using the words "like" or "as." "Gloomy as the night" is the simile here, since his sadness is being compared to nighttime.
