The St Anthony was the personal property of King John III of Portugal and the flagship of his fleet. She was a carrack; these were largest ships of the time and the first truly ocean going vessels. The cargo was particularly valuable, estimated to be worth at the time £18,800 (about 4,000 times a man's annual wage), and it is thought to have included the dowry of Princess Katherine, bride of King John III and sister of Charles V, the Holy Roman Emperor. The cargo manifest survives.