This drawing shows the fortress of Diu, located on an island off the northwest coast of India. In 1509, the Portuguese defeated the forces of the Sultan of Gujarat in the Battle of Diu, thereby securing dominance over trade routes in the Indian Ocean. Construction of this fortress-garrison complex began in 1535, under an agreement with the sultan, but the agreement fell apart and the sultan’s troops attacked the fort in 1537. The fortress was reconstructed in 1545 by João de Castro (1500-48), a Portuguese naval commander and the fourth viceroy of Portuguese India.