Why is Othello summoned before the Duke of Venice for his marriage?

Othello is a Moor living in Venice. He is a powerful and respected general, but his dark skin still renders him an outsider. As such, he woos Desdemona, the daughter of a powerful Venetian, in secret, using Cassio as a go-between. When her father discovers of the marriage, Desdemona and Othello are called to the Duke of Venice to explain themselves.