Collectively, all the curved wooden or metal pieces of a ship’s hull that lie perpendicularly to the keel and receive the planking. Their design varies according to the historical period and type of architecture. During classical antiquity, especially in the Mediterranean, ships were built by first assembling planks to form the hull which was then strengthened by the addition of frames. This type of construction is known as ‘shell-first’. In the Middle Ages, with the rise of the construction method of building the frames and subsequently adding the planking (frames-first), each individual frame comprised a floor, two futtocks and two or more top timbers. See the diagrams Hull and Shell-first.