The first recorded mention of the use of a "line of battle" tactic is attested from 1500. The "Instructions" provided in 1500 by King Manuel I of Portugal to the commander of a fleet dispatched to the Indian Ocean suggests its use predated the written instructions. Portuguese fleets overseas deployed in line ahead, firing one broadside and then putting about in order to return and discharge the other, resolving battles by gunnery alone. In a treatise of 1555, "The Art of War at Sea", Portuguese theorist on naval warfare and shipbuilding, Fernão de Oliveira, recognized that at sea, the Portuguese "fight at a distance, as if from walls and fortresses...". He recommended the single line ahead as the ideal combat formation.