In the castle at Pavia, Adelaide receives the German King Lotario, who has not only brought his army to her aid but loves her too. She accepts his aid and urges him to fight Berengario and Matilde. He will do so, he says, if she will repay him with her love (Aria:"Rammentati, cor mio"). Clorimondo, Berengario's general, appears to Adelaide and tells her she must either marry the son or be killed by the father (Aria:"Se il mar promette calma") but Adelaide puts her trust in Lotario (Aria:"Quel cor che mi donasti").