A Venetian ambassador of that time praised Marguerite as knowing all the secrets of diplomatic art, hence to be treated with deference and circumspection. Marguerite's most remarkable adventure involved freeing her brother, King Francis I, who had been held prisoner in Spain by Charles V, Holy Roman Emperor after being captured in the Battle of Pavia, Italy, 1525. During a critical period of the negotiations, Queen Marguerite rode horseback through wintry woods, twelve hours a day for many days, to meet a safe-conduct deadline, while writing her diplomatic letters at night.