1 Melting in tears, then gan she thus lament:

gan > did

2 "The wretched woman, whom unhappy hour 3 Has now made thrall to your commandment,

thrall > slave commandment > authority, control

4 Before angry heavens list to lour,

list > chose, pleased

5 And fortune false betrayed me to your power, 6 Was (O what now avails that I was?)

that > [that which, what]

7 Born the sole daughter of an emperor, 8 He that the wide west under his rule has, 9 And high has set his throne where the Tiber does pass.

the Tiber > (The River Tiber: an overt reference to Rome)