Final answer:
The document by Duarte Barbosa describes how Muslim merchants controlled Calicut's trade before the Portuguese transformed Indian Ocean maritime trade, subsequently causing many Muslim traders to leave Calicut.
Step-by-step explanation:
The account by Duarte Barbosa emphasizes that prior to the arrival of the Portuguese, Calicut was a prosperous trading center dominated by Muslim merchants from various regions, including Arabs, Persians, and Gujaratis. This dominance in trade, however, was challenged when the Portuguese transformed maritime trade in the Indian Ocean during the sixteenth century, taking control over sea trade and causing many Muslim traders to depart from Calicut.
The document likely serves as an eyewitness account and an official report detailing the changes in Calicut's trade and social dynamics due to Portuguese intervention, which could have been used to inform the Portuguese crown and other officials about the effectiveness of their maritime policies in the region.